Cleaning up normalization of DISCO convolutions

examples/train_sfno.py

@@ -430,21 +430,21 @@ def main(train=True, load_checkpoint=False, enable_amp=False, log_grads=0):
         normalization_layer="none",
     )
 
-    models[f"lsno_sc2_layers4_e32"] = partial(
-        LSNO,
-        spectral_transform="sht",
-        img_size=(nlat, nlon),
-        grid=grid,
-        num_layers=4,
-        scale_factor=2,
-        embed_dim=32,
-        operator_type="driscoll-healy",
-        activation_function="gelu",
-        big_skip=True,
-        pos_embed=False,
-        use_mlp=True,
-        normalization_layer="none",
-    )
+    # models[f"lsno_sc2_layers4_e32"] = partial(
+    #     LSNO,
+    #     spectral_transform="sht",
+    #     img_size=(nlat, nlon),
+    #     grid=grid,
+    #     num_layers=4,
+    #     scale_factor=2,
+    #     embed_dim=32,
+    #     operator_type="driscoll-healy",
+    #     activation_function="gelu",
+    #     big_skip=True,
+    #     pos_embed=False,
+    #     use_mlp=True,
+    #     normalization_layer="none",
+    # )
 
     # iterate over models and train each model
     root_path = os.path.dirname(__file__)

notebooks/plotting.py

@@ -40,8 +40,8 @@ def plot_sphere(data,
                 title=None,
                 colorbar=False,
                 coastlines=False,
-                central_latitude=20,
-                central_longitude=20,
+                central_latitude=0,
+                central_longitude=0,
                 lon=None,
                 lat=None,
                 **kwargs):
@@ -74,14 +74,15 @@ def plot_sphere(data,
     return im
 
 def plot_data(data,
-              fig=None,
-              projection=None,
-              cmap="RdBu",
-              title=None,
-              colorbar=False,
-              lon=None,
-              lat=None,
-              **kwargs):
+                fig=None,
+                cmap="RdBu",
+                title=None,
+                colorbar=False,
+                coastlines=False,
+                central_longitude=0,
+                lon=None,
+                lat=None,
+                **kwargs):
     if fig == None:
         fig = plt.figure()
 
@@ -93,16 +94,19 @@ def plot_data(data,
         lat = np.linspace(np.pi/2., -np.pi/2., nlat)
     Lon, Lat = np.meshgrid(lon, lat)
 
-    fig = plt.figure(figsize=(10, 5))
-    ax = fig.add_subplot(1, 1, 1, projection=projection)
-    im = ax.pcolormesh(Lon, Lat, data, cmap=cmap, **kwargs)
+    proj = ccrs.PlateCarree(central_longitude=central_longitude)
+    # proj = ccrs.Mollweide(central_longitude=central_longitude)
+
+    ax = fig.add_subplot(projection=proj)
+    Lon = Lon*180/np.pi
+    Lat = Lat*180/np.pi
 
+    # contour data over the map.
+    im = ax.pcolormesh(Lon, Lat, data, cmap=cmap, transform=ccrs.PlateCarree(), antialiased=False, **kwargs)
+    if coastlines:
+        ax.add_feature(cartopy.feature.COASTLINE, edgecolor='white', facecolor='none', linewidth=1.5)
     if colorbar:
         plt.colorbar(im)
     plt.title(title, y=1.05)
 
-    ax.grid(True)
-    ax.set_xticklabels([])
-    ax.set_yticklabels([])
-
     return im
\ No newline at end of file

tests/test_convolution.py

@@ -41,92 +41,110 @@ from torch_harmonics import *
 from torch_harmonics.quadrature import _precompute_grid, _precompute_latitudes
 
 
-def _compute_vals_isotropic(r: torch.Tensor, phi: torch.Tensor, nr: int, r_cutoff: float):
-    """
-    helper routine to compute the values of the isotropic kernel densely
-    """
-
-    kernel_size = (nr // 2) + nr % 2
-    ikernel = torch.arange(kernel_size).reshape(-1, 1, 1)
-    dr = 2 * r_cutoff / (nr + 1)
-
-    # compute the support
-    if nr % 2 == 1:
-        ir = ikernel * dr
-    else:
-        ir = (ikernel + 0.5) * dr
-
-    vals = torch.where(
-        ((r - ir).abs() <= dr) & (r <= r_cutoff),
-        (1 - (r - ir).abs() / dr),
-        0,
-    )
-
-    return vals
-
-
-def _compute_vals_anisotropic(r: torch.Tensor, phi: torch.Tensor, nr: int, nphi: int, r_cutoff: float):
-    """
-    helper routine to compute the values of the anisotropic kernel densely
-    """
-
-    kernel_size = (nr // 2) * nphi + nr % 2
-    ikernel = torch.arange(kernel_size).reshape(-1, 1, 1)
-    dr = 2 * r_cutoff / (nr + 1)
-    dphi = 2.0 * math.pi / nphi
-
-    # disambiguate even and uneven cases and compute the support
-    if nr % 2 == 1:
-        ir = ((ikernel - 1) // nphi + 1) * dr
-        iphi = ((ikernel - 1) % nphi) * dphi
-    else:
-        ir = (ikernel // nphi + 0.5) * dr
-        iphi = (ikernel % nphi) * dphi
-
-    # compute the value of the filter
-    if nr % 2 == 1:
-        # find the indices where the rotated position falls into the support of the kernel
-        cond_r = ((r - ir).abs() <= dr) & (r <= r_cutoff)
-        cond_phi = ((phi - iphi).abs() <= dphi) | ((2 * math.pi - (phi - iphi).abs()) <= dphi)
-        r_vals = torch.where(cond_r, (1 - (r - ir).abs() / dr), 0.0)
-        phi_vals = torch.where(cond_phi, (1 - torch.minimum((phi - iphi).abs(), (2 * math.pi - (phi - iphi).abs())) / dphi), 0.0)
-        vals = torch.where(ikernel > 0, r_vals * phi_vals, r_vals)
-    else:
-        # find the indices where the rotated position falls into the support of the kernel
-        cond_r = ((r - ir).abs() <= dr) & (r <= r_cutoff)
-        cond_phi = ((phi - iphi).abs() <= dphi) | ((2 * math.pi - (phi - iphi).abs()) <= dphi)
-        r_vals = torch.where(cond_r, (1 - (r - ir).abs() / dr), 0.0)
-        phi_vals = torch.where(cond_phi, (1 - torch.minimum((phi - iphi).abs(), (2 * math.pi - (phi - iphi).abs())) / dphi), 0.0)
-        vals = r_vals * phi_vals
-
-        # in the even case, the inner casis functions overlap into areas with a negative areas
-        rn = -r
-        phin = torch.where(phi + math.pi >= 2 * math.pi, phi - math.pi, phi + math.pi)
-        cond_rn = ((rn - ir).abs() <= dr) & (rn <= r_cutoff)
-        cond_phin = ((phin - iphi).abs() <= dphi) | ((2 * math.pi - (phin - iphi).abs()) <= dphi)
-        rn_vals = torch.where(cond_rn, (1 - (rn - ir).abs() / dr), 0.0)
-        phin_vals = torch.where(cond_phin, (1 - torch.minimum((phin - iphi).abs(), (2 * math.pi - (phin - iphi).abs())) / dphi), 0.0)
-        vals += rn_vals * phin_vals
-
-    return vals
-
-
-def _normalize_convolution_tensor_dense(psi, quad_weights, transpose_normalization=False, merge_quadrature=False, eps=1e-9):
+# def _compute_vals_isotropic(r: torch.Tensor, phi: torch.Tensor, nr: int, r_cutoff: float):
+#     """
+#     helper routine to compute the values of the isotropic kernel densely
+#     """
+
+#     kernel_size = (nr // 2) + nr % 2
+#     ikernel = torch.arange(kernel_size).reshape(-1, 1, 1)
+#     dr = 2 * r_cutoff / (nr + 1)
+
+#     # compute the support
+#     if nr % 2 == 1:
+#         ir = ikernel * dr
+#     else:
+#         ir = (ikernel + 0.5) * dr
+
+#     vals = torch.where(
+#         ((r - ir).abs() <= dr) & (r <= r_cutoff),
+#         (1 - (r - ir).abs() / dr),
+#         0,
+#     )
+
+#     return vals
+
+
+# def _compute_vals_anisotropic(r: torch.Tensor, phi: torch.Tensor, nr: int, nphi: int, r_cutoff: float):
+#     """
+#     helper routine to compute the values of the anisotropic kernel densely
+#     """
+
+#     kernel_size = (nr // 2) * nphi + nr % 2
+#     ikernel = torch.arange(kernel_size).reshape(-1, 1, 1)
+#     dr = 2 * r_cutoff / (nr + 1)
+#     dphi = 2.0 * math.pi / nphi
+
+#     # disambiguate even and uneven cases and compute the support
+#     if nr % 2 == 1:
+#         ir = ((ikernel - 1) // nphi + 1) * dr
+#         iphi = ((ikernel - 1) % nphi) * dphi
+#     else:
+#         ir = (ikernel // nphi + 0.5) * dr
+#         iphi = (ikernel % nphi) * dphi
+
+#     # compute the value of the filter
+#     if nr % 2 == 1:
+#         # find the indices where the rotated position falls into the support of the kernel
+#         cond_r = ((r - ir).abs() <= dr) & (r <= r_cutoff)
+#         cond_phi = ((phi - iphi).abs() <= dphi) | ((2 * math.pi - (phi - iphi).abs()) <= dphi)
+#         r_vals = torch.where(cond_r, (1 - (r - ir).abs() / dr), 0.0)
+#         phi_vals = torch.where(cond_phi, (1 - torch.minimum((phi - iphi).abs(), (2 * math.pi - (phi - iphi).abs())) / dphi), 0.0)
+#         vals = torch.where(ikernel > 0, r_vals * phi_vals, r_vals)
+#     else:
+#         # find the indices where the rotated position falls into the support of the kernel
+#         cond_r = ((r - ir).abs() <= dr) & (r <= r_cutoff)
+#         cond_phi = ((phi - iphi).abs() <= dphi) | ((2 * math.pi - (phi - iphi).abs()) <= dphi)
+#         r_vals = torch.where(cond_r, (1 - (r - ir).abs() / dr), 0.0)
+#         phi_vals = torch.where(cond_phi, (1 - torch.minimum((phi - iphi).abs(), (2 * math.pi - (phi - iphi).abs())) / dphi), 0.0)
+#         vals = r_vals * phi_vals
+
+#         # in the even case, the inner casis functions overlap into areas with a negative areas
+#         rn = -r
+#         phin = torch.where(phi + math.pi >= 2 * math.pi, phi - math.pi, phi + math.pi)
+#         cond_rn = ((rn - ir).abs() <= dr) & (rn <= r_cutoff)
+#         cond_phin = ((phin - iphi).abs() <= dphi) | ((2 * math.pi - (phin - iphi).abs()) <= dphi)
+#         rn_vals = torch.where(cond_rn, (1 - (rn - ir).abs() / dr), 0.0)
+#         phin_vals = torch.where(cond_phin, (1 - torch.minimum((phin - iphi).abs(), (2 * math.pi - (phin - iphi).abs())) / dphi), 0.0)
+#         vals += rn_vals * phin_vals
+
+#     return vals
+
+
+def _normalize_convolution_tensor_dense(psi, quad_weights, transpose_normalization=False, basis_norm_mode="none", merge_quadrature=False, eps=1e-9):
     """
     Discretely normalizes the convolution tensor.
     """
 
     kernel_size, nlat_out, nlon_out, nlat_in, nlon_in = psi.shape
-    scale_factor = float(nlon_in // nlon_out)
+    correction_factor = nlon_out / nlon_in
+
+    if basis_norm_mode == "individual":
+        if transpose_normalization:
+            # the normalization is not quite symmetric due to the compressed way psi is stored in the main code
+            # look at the normalization code in the actual implementation
+            psi_norm = torch.sqrt(torch.sum(quad_weights.reshape(1, -1, 1, 1, 1) * psi[:, :, :1].abs().pow(2), dim=(1, 4), keepdim=True) / 4 / math.pi)
+        else:
+            psi_norm = torch.sqrt(torch.sum(quad_weights.reshape(1, 1, 1, -1, 1) * psi.abs().pow(2), dim=(3, 4), keepdim=True) / 4 / math.pi)
+
+    elif basis_norm_mode == "mean":
+        if transpose_normalization:
+            # the normalization is not quite symmetric due to the compressed way psi is stored in the main code
+            # look at the normalization code in the actual implementation
+            psi_norm = torch.sqrt(torch.sum(quad_weights.reshape(1, -1, 1, 1, 1) * psi[:, :, :1].abs().pow(2), dim=(1, 4), keepdim=True) / 4 / math.pi)
+            psi_norm = psi_norm.mean(dim=3, keepdim=True)
+        else:
+            psi_norm = torch.sqrt(torch.sum(quad_weights.reshape(1, 1, 1, -1, 1) * psi.abs().pow(2), dim=(3, 4), keepdim=True) / 4 / math.pi)
+            psi_norm = psi_norm.mean(dim=1, keepdim=True)
+    elif basis_norm_mode == "none":
+        psi_norm = 1.0
+    else:
+        raise ValueError(f"Unknown basis normalization mode {basis_norm_mode}.")
 
     if transpose_normalization:
-        # the normalization is not quite symmetric due to the compressed way psi is stored in the main code
-        # look at the normalization code in the actual implementation
-        psi_norm = torch.sum(quad_weights.reshape(1, -1, 1, 1, 1) * psi[:, :, :1], dim=(1, 4), keepdim=True) / scale_factor
         if merge_quadrature:
-            psi = quad_weights.reshape(1, -1, 1, 1, 1) * psi
+            psi = quad_weights.reshape(1, -1, 1, 1, 1) * psi / correction_factor
     else:
-        psi_norm = torch.sum(quad_weights.reshape(1, 1, 1, -1, 1) * psi, dim=(3, 4), keepdim=True)
         if merge_quadrature:
             psi = quad_weights.reshape(1, 1, 1, -1, 1) * psi
 
@@ -137,11 +155,12 @@ def _precompute_convolution_tensor_dense(
     in_shape,
     out_shape,
     kernel_shape,
-    quad_weights,
+    filter_basis,
     grid_in="equiangular",
     grid_out="equiangular",
     theta_cutoff=0.01 * math.pi,
     transpose_normalization=False,
+    basis_norm_mode="none",
     merge_quadrature=False,
 ):
     """
@@ -151,29 +170,26 @@ def _precompute_convolution_tensor_dense(
     assert len(in_shape) == 2
     assert len(out_shape) == 2
 
-    quad_weights = quad_weights.reshape(-1, 1)
-
-    if len(kernel_shape) == 1:
-        kernel_handle = partial(_compute_vals_isotropic, nr=kernel_shape[0], r_cutoff=theta_cutoff)
-        kernel_size = math.ceil(kernel_shape[0] / 2)
-    elif len(kernel_shape) == 2:
-        kernel_handle = partial(_compute_vals_anisotropic, nr=kernel_shape[0], nphi=kernel_shape[1], r_cutoff=theta_cutoff)
-        kernel_size = (kernel_shape[0] // 2) * kernel_shape[1] + kernel_shape[0] % 2
-    else:
-        raise ValueError("kernel_shape should be either one- or two-dimensional.")
+    kernel_size = filter_basis.kernel_size
 
     nlat_in, nlon_in = in_shape
     nlat_out, nlon_out = out_shape
 
-    lats_in, _ = quadrature._precompute_latitudes(nlat_in, grid=grid_in)
+    lats_in, win = quadrature._precompute_latitudes(nlat_in, grid=grid_in)
     lats_in = torch.from_numpy(lats_in).float()
-    lats_out, _ = quadrature._precompute_latitudes(nlat_out, grid=grid_out)
+    lats_out, wout = quadrature._precompute_latitudes(nlat_out, grid=grid_out)
     lats_out = torch.from_numpy(lats_out).float()  # array for accumulating non-zero indices
 
     # compute the phi differences. We need to make the linspace exclusive to not double the last point
     lons_in = torch.linspace(0, 2 * math.pi, nlon_in + 1)[:-1]
     lons_out = torch.linspace(0, 2 * math.pi, nlon_out + 1)[:-1]
 
+    # compute quadrature weights that will be merged into the Psi tensor
+    if transpose_normalization:
+        quad_weights = 2.0 * torch.pi * torch.from_numpy(wout).float().reshape(-1, 1) / nlon_in
+    else:
+        quad_weights = 2.0 * torch.pi * torch.from_numpy(win).float().reshape(-1, 1) / nlon_in
+
     out = torch.zeros(kernel_size, nlat_out, nlon_out, nlat_in, nlon_in)
 
     for t in range(nlat_out):
@@ -187,7 +203,7 @@ def _precompute_convolution_tensor_dense(
 
             # compute cartesian coordinates of the rotated position
             x = torch.cos(alpha) * torch.cos(beta) * torch.sin(gamma) + torch.cos(gamma) * torch.sin(alpha)
-            y = torch.sin(beta) * torch.sin(gamma)
+            y = torch.sin(beta) * torch.sin(gamma) * torch.ones_like(alpha)
 
             # normalize instead of clipping to ensure correct range
             norm = torch.sqrt(x * x + y * y + z * z)
@@ -197,13 +213,17 @@ def _precompute_convolution_tensor_dense(
 
             # compute spherical coordinates
             theta = torch.arccos(z)
-            phi = torch.arctan2(y, x) + torch.pi
+            phi = torch.arctan2(y, x)
+            phi = torch.where(phi < 0.0, phi + 2 * torch.pi, phi)
 
             # find the indices where the rotated position falls into the support of the kernel
-            out[:, t, p, :, :] = kernel_handle(theta, phi)
+            iidx, vals = filter_basis.compute_support_vals(theta, phi, r_cutoff=theta_cutoff)
+            out[iidx[:, 0], t, p, iidx[:, 1], iidx[:, 2]] = vals
 
     # take care of normalization
-    out = _normalize_convolution_tensor_dense(out, quad_weights=quad_weights, transpose_normalization=transpose_normalization, merge_quadrature=merge_quadrature)
+    out = _normalize_convolution_tensor_dense(
+        out, quad_weights=quad_weights, transpose_normalization=transpose_normalization, basis_norm_mode=basis_norm_mode, merge_quadrature=merge_quadrature
+    )
 
     return out
 
@@ -217,30 +237,32 @@ class TestDiscreteContinuousConvolution(unittest.TestCase):
         else:
             self.device = torch.device("cpu")
 
-        torch.manual_seed(333)
+        self.device = torch.device("cpu")
 
     @parameterized.expand(
         [
             # regular convolution
-            [8, 4, 2, (16, 32), (16, 32), [3], "equiangular", "equiangular", False, 1e-4],
-            [8, 4, 2, (16, 32), (8, 16), [5], "equiangular", "equiangular", False, 1e-4],
-            [8, 4, 2, (16, 32), (8, 16), [3, 3], "equiangular", "equiangular", False, 1e-4],
-            [8, 4, 2, (16, 32), (8, 16), [4, 3], "equiangular", "equiangular", False, 1e-4],
-            [8, 4, 2, (16, 24), (8, 8), [3], "equiangular", "equiangular", False, 1e-4],
-            [8, 4, 2, (18, 36), (6, 12), [7], "equiangular", "equiangular", False, 1e-4],
-            [8, 4, 2, (16, 32), (8, 16), [5], "equiangular", "legendre-gauss", False, 1e-4],
-            [8, 4, 2, (16, 32), (8, 16), [5], "legendre-gauss", "equiangular", False, 1e-4],
-            [8, 4, 2, (16, 32), (8, 16), [5], "legendre-gauss", "legendre-gauss", False, 1e-4],
+            [8, 4, 2, (16, 32), (16, 32), [3], "piecewise linear", "mean", "equiangular", "equiangular", False, 1e-4],
+            [8, 4, 2, (16, 32), (8, 16), [3], "piecewise linear", "mean", "equiangular", "equiangular", False, 1e-4],
+            [8, 4, 2, (24, 48), (12, 24), [3, 3], "piecewise linear", "mean", "equiangular", "equiangular", False, 1e-4],
+            [8, 4, 2, (24, 48), (12, 24), [4, 3], "piecewise linear", "mean", "equiangular", "equiangular", False, 1e-4],
+            [8, 4, 2, (24, 48), (12, 24), [2, 2], "morlet", "mean", "equiangular", "equiangular", False, 1e-4],
+            [8, 4, 2, (16, 24), (8, 8), [3], "piecewise linear", "mean", "equiangular", "equiangular", False, 1e-4],
+            [8, 4, 2, (18, 36), (6, 12), [7], "piecewise linear", "mean", "equiangular", "equiangular", False, 1e-4],
+            [8, 4, 2, (16, 32), (8, 16), [5], "piecewise linear", "mean", "equiangular", "legendre-gauss", False, 1e-4],
+            [8, 4, 2, (16, 32), (8, 16), [5], "piecewise linear", "mean", "legendre-gauss", "equiangular", False, 1e-4],
+            [8, 4, 2, (16, 32), (8, 16), [5], "piecewise linear", "mean", "legendre-gauss", "legendre-gauss", False, 1e-4],
             # transpose convolution
-            [8, 4, 2, (16, 32), (16, 32), [3], "equiangular", "equiangular", True, 1e-4],
-            [8, 4, 2, (8, 16), (16, 32), [5], "equiangular", "equiangular", True, 1e-4],
-            [8, 4, 2, (8, 16), (16, 32), [3, 3], "equiangular", "equiangular", True, 1e-4],
-            [8, 4, 2, (8, 16), (16, 32), [4, 3], "equiangular", "equiangular", True, 1e-4],
-            [8, 4, 2, (8, 8), (16, 24), [3], "equiangular", "equiangular", True, 1e-4],
-            [8, 4, 2, (6, 12), (18, 36), [7], "equiangular", "equiangular", True, 1e-4],
-            [8, 4, 2, (8, 16), (16, 32), [5], "equiangular", "legendre-gauss", True, 1e-4],
-            [8, 4, 2, (8, 16), (16, 32), [5], "legendre-gauss", "equiangular", True, 1e-4],
-            [8, 4, 2, (8, 16), (16, 32), [5], "legendre-gauss", "legendre-gauss", True, 1e-4],
+            [8, 4, 2, (16, 32), (16, 32), [3], "piecewise linear", "mean", "equiangular", "equiangular", True, 1e-4],
+            [8, 4, 2, (8, 16), (16, 32), [5], "piecewise linear", "mean", "equiangular", "equiangular", True, 1e-4],
+            [8, 4, 2, (12, 24), (24, 48), [3, 3], "piecewise linear", "mean", "equiangular", "equiangular", True, 1e-4],
+            [8, 4, 2, (12, 24), (24, 48), [4, 3], "piecewise linear", "mean", "equiangular", "equiangular", True, 1e-4],
+            [8, 4, 2, (12, 24), (24, 48), [2, 2], "morlet", "mean", "equiangular", "equiangular", True, 1e-4],
+            [8, 4, 2, (8, 8), (16, 24), [3], "piecewise linear", "mean", "equiangular", "equiangular", True, 1e-4],
+            [8, 4, 2, (6, 12), (18, 36), [7], "piecewise linear", "mean", "equiangular", "equiangular", True, 1e-4],
+            [8, 4, 2, (8, 16), (16, 32), [5], "piecewise linear", "mean", "equiangular", "legendre-gauss", True, 1e-4],
+            [8, 4, 2, (8, 16), (16, 32), [5], "piecewise linear", "mean", "legendre-gauss", "equiangular", True, 1e-4],
+            [8, 4, 2, (8, 16), (16, 32), [5], "piecewise linear", "mean", "legendre-gauss", "legendre-gauss", True, 1e-4],
         ]
     )
     def test_disco_convolution(
@@ -251,6 +273,8 @@ class TestDiscreteContinuousConvolution(unittest.TestCase):
         in_shape,
         out_shape,
         kernel_shape,
+        basis_type,
+        basis_norm_mode,
         grid_in,
         grid_out,
         transpose,
@@ -259,19 +283,38 @@ class TestDiscreteContinuousConvolution(unittest.TestCase):
         nlat_in, nlon_in = in_shape
         nlat_out, nlon_out = out_shape
 
-        theta_cutoff = (kernel_shape[0] + 1) / 2 * torch.pi / float(nlat_out - 1)
+        theta_cutoff = (kernel_shape[0] + 1) * torch.pi / float(nlat_in - 1)
 
         Conv = DiscreteContinuousConvTransposeS2 if transpose else DiscreteContinuousConvS2
-        conv = Conv(in_channels, out_channels, in_shape, out_shape, kernel_shape, groups=1, grid_in=grid_in, grid_out=grid_out, bias=False, theta_cutoff=theta_cutoff).to(
-            self.device
-        )
-
-        _, wgl = _precompute_latitudes(nlat_in, grid=grid_in)
-        quad_weights = 2.0 * torch.pi * torch.from_numpy(wgl).float().reshape(-1, 1) / nlon_in
+        conv = Conv(
+            in_channels,
+            out_channels,
+            in_shape,
+            out_shape,
+            kernel_shape,
+            basis_type=basis_type,
+            basis_norm_mode=basis_norm_mode,
+            groups=1,
+            grid_in=grid_in,
+            grid_out=grid_out,
+            bias=False,
+            theta_cutoff=theta_cutoff,
+        ).to(self.device)
+
+        filter_basis = conv.filter_basis
 
         if transpose:
             psi_dense = _precompute_convolution_tensor_dense(
-                out_shape, in_shape, kernel_shape, quad_weights, grid_in=grid_out, grid_out=grid_in, theta_cutoff=theta_cutoff, transpose_normalization=True, merge_quadrature=True
+                out_shape,
+                in_shape,
+                kernel_shape,
+                filter_basis,
+                grid_in=grid_out,
+                grid_out=grid_in,
+                theta_cutoff=theta_cutoff,
+                transpose_normalization=transpose,
+                basis_norm_mode=basis_norm_mode,
+                merge_quadrature=True,
             ).to(self.device)
 
             psi = torch.sparse_coo_tensor(conv.psi_idx, conv.psi_vals, size=(conv.kernel_size, conv.nlat_in, conv.nlat_out * conv.nlon_out)).to_dense()
@@ -279,7 +322,16 @@ class TestDiscreteContinuousConvolution(unittest.TestCase):
             self.assertTrue(torch.allclose(psi, psi_dense[:, :, 0].reshape(-1, nlat_in, nlat_out * nlon_out)))
         else:
             psi_dense = _precompute_convolution_tensor_dense(
-                in_shape, out_shape, kernel_shape, quad_weights, grid_in=grid_in, grid_out=grid_out, theta_cutoff=theta_cutoff, transpose_normalization=False, merge_quadrature=True
+                in_shape,
+                out_shape,
+                kernel_shape,
+                filter_basis,
+                grid_in=grid_in,
+                grid_out=grid_out,
+                theta_cutoff=theta_cutoff,
+                transpose_normalization=transpose,
+                basis_norm_mode=basis_norm_mode,
+                merge_quadrature=True,
             ).to(self.device)
 
             psi = torch.sparse_coo_tensor(conv.psi_idx, conv.psi_vals, size=(conv.kernel_size, conv.nlat_out, conv.nlat_in * conv.nlon_in)).to_dense()

tests/test_distributed_convolution.py

@@ -183,21 +183,23 @@ class TestDistributedDiscreteContinuousConvolution(unittest.TestCase):
 
     @parameterized.expand(
         [
-            [128, 256, 128, 256, 32, 8, [3], 1, "equiangular", "equiangular", False, 1e-5],
-            [129, 256, 128, 256, 32, 8, [3], 1, "equiangular", "equiangular", False, 1e-5],
-            [128, 256, 128, 256, 32, 8, [3, 2], 1, "equiangular", "equiangular", False, 1e-5],
-            [128, 256, 64, 128, 32, 8, [3], 1, "equiangular", "equiangular", False, 1e-5],
-            [128, 256, 128, 256, 32, 8, [3], 2, "equiangular", "equiangular", False, 1e-5],
-            [128, 256, 128, 256, 32, 6, [3], 1, "equiangular", "equiangular", False, 1e-5],
-            [128, 256, 128, 256, 32, 8, [3], 1, "equiangular", "equiangular", True, 1e-5],
-            [129, 256, 129, 256, 32, 8, [3], 1, "equiangular", "equiangular", True, 1e-5],
-            [128, 256, 128, 256, 32, 8, [3, 2], 1, "equiangular", "equiangular", True, 1e-5],
-            [64, 128, 128, 256, 32, 8, [3], 1, "equiangular", "equiangular", True, 1e-5],
-            [128, 256, 128, 256, 32, 8, [3], 2, "equiangular", "equiangular", True, 1e-5],
-            [128, 256, 128, 256, 32, 6, [3], 1, "equiangular", "equiangular", True, 1e-5],
+            [128, 256, 128, 256, 32, 8, [3], "piecewise linear", "individual", 1, "equiangular", "equiangular", False, 1e-5],
+            [129, 256, 128, 256, 32, 8, [3], "piecewise linear", "individual", 1, "equiangular", "equiangular", False, 1e-5],
+            [128, 256, 128, 256, 32, 8, [3, 2], "piecewise linear", "individual", 1, "equiangular", "equiangular", False, 1e-5],
+            [128, 256, 64, 128, 32, 8, [3], "piecewise linear", "individual", 1, "equiangular", "equiangular", False, 1e-5],
+            [128, 256, 128, 256, 32, 8, [3], "piecewise linear", "individual", 2, "equiangular", "equiangular", False, 1e-5],
+            [128, 256, 128, 256, 32, 6, [3], "piecewise linear", "individual", 1, "equiangular", "equiangular", False, 1e-5],
+            [128, 256, 128, 256, 32, 8, [3], "piecewise linear", "individual", 1, "equiangular", "equiangular", True, 1e-5],
+            [129, 256, 129, 256, 32, 8, [3], "piecewise linear", "individual", 1, "equiangular", "equiangular", True, 1e-5],
+            [128, 256, 128, 256, 32, 8, [3, 2], "piecewise linear", "individual", 1, "equiangular", "equiangular", True, 1e-5],
+            [64, 128, 128, 256, 32, 8, [3], "piecewise linear", "individual", 1, "equiangular", "equiangular", True, 1e-5],
+            [128, 256, 128, 256, 32, 8, [3], "piecewise linear", "individual", 2, "equiangular", "equiangular", True, 1e-5],
+            [128, 256, 128, 256, 32, 6, [3], "piecewise linear", "individual", 1, "equiangular", "equiangular", True, 1e-5],
         ]
     )
-    def test_distributed_disco_conv(self, nlat_in, nlon_in, nlat_out, nlon_out, batch_size, num_chan, kernel_shape, groups, grid_in, grid_out, transpose, tol):
+    def test_distributed_disco_conv(
+        self, nlat_in, nlon_in, nlat_out, nlon_out, batch_size, num_chan, kernel_shape, basis_type, basis_norm_mode, groups, grid_in, grid_out, transpose, tol
+    ):
 
         B, C, H, W = batch_size, num_chan, nlat_in, nlon_in
 
@@ -206,6 +208,8 @@ class TestDistributedDiscreteContinuousConvolution(unittest.TestCase):
             out_channels=C,
             in_shape=(nlat_in, nlon_in),
             out_shape=(nlat_out, nlon_out),
+            basis_type=basis_type,
+            basis_norm_mode=basis_norm_mode,
             kernel_shape=kernel_shape,
             groups=groups,
             grid_in=grid_in,

torch_harmonics/convolution.py

@@ -57,70 +57,71 @@ except ImportError as err:
 
 
 def _normalize_convolution_tensor_s2(
-    psi_idx, psi_vals, in_shape, out_shape, kernel_size, quad_weights, transpose_normalization=False, basis_norm_mode="sum", merge_quadrature=False, eps=1e-9
+    psi_idx, psi_vals, in_shape, out_shape, kernel_size, quad_weights, transpose_normalization=False, basis_norm_mode="none", merge_quadrature=False, eps=1e-9
 ):
     """
-    Discretely normalizes the convolution tensor. Supports different normalization modes
+    Discretely normalizes the convolution tensor and pre-applies quadrature weights. Supports the following three normalization modes:
+    - "none": No normalization is applied.
+    - "individual": for each output latitude and filter basis function the filter is numerically integrated over the sphere and normalized so that it yields 1.
+    - "mean": the norm is computed for each output latitude and then averaged over the output latitudes. Each basis function is then normalized by this mean.
     """
 
-    nlat_in, nlon_in = in_shape
-    nlat_out, nlon_out = out_shape
+    # reshape the indices implicitly to be ikernel, out_shape[0], in_shape[0], in_shape[1]
+    idx = torch.stack([psi_idx[0], psi_idx[1], psi_idx[2] // in_shape[1], psi_idx[2] % in_shape[1]], dim=0)
 
-    # reshape the indices implicitly to be ikernel, lat_out, lat_in, lon_in
-    idx = torch.stack([psi_idx[0], psi_idx[1], psi_idx[2] // nlon_in, psi_idx[2] % nlon_in], dim=0)
+    # getting indices for adressing kernels, input and output latitudes
+    ikernel = idx[0]
 
     if transpose_normalization:
-        # pre-compute the quadrature weights
-        q = quad_weights[idx[1]].reshape(-1)
-
-        # loop through dimensions which require normalization
-        for ik in range(kernel_size):
-            for ilat in range(nlat_in):
-
-                # get relevant entries depending on the normalization mode
-                if basis_norm_mode == "individual":
-
-                    iidx = torch.argwhere((idx[0] == ik) & (idx[2] == ilat))
-                    # normalize, while summing also over the input longitude dimension here as this is not available for the output
-                    vnorm = torch.sum(psi_vals[iidx].abs() * q[iidx])
-                elif basis_norm_mode == "sum":
-                    # this will perform repeated normalization in the kernel dimension but this shouldn't lead to issues
-                    iidx = torch.argwhere(idx[2] == ilat)
-                    # normalize, while summing also over the input longitude dimension here as this is not available for the output
-                    vnorm = torch.sum(psi_vals[iidx].abs() * q[iidx])
-                else:
-                    raise ValueError(f"Unknown basis normalization mode {basis_norm_mode}.")
-
-                if merge_quadrature:
-                    # the correction factor accounts for the difference in longitudinal grid points when the input vector is upscaled
-                    psi_vals[iidx] = psi_vals[iidx] * q[iidx] * nlon_in / nlon_out / (vnorm + eps)
-                else:
-                    psi_vals[iidx] = psi_vals[iidx] / (vnorm + eps)
+        ilat_out = idx[2]
+        ilat_in = idx[1]
+        # here we are deliberately swapping input and output shapes to handle transpose normalization with the same code
+        nlat_out = in_shape[0]
+        correction_factor = out_shape[1] / in_shape[1]
     else:
-        # pre-compute the quadrature weights
-        q = quad_weights[idx[2]].reshape(-1)
-
-        # loop through dimensions which require normalization
-        for ik in range(kernel_size):
-            for ilat in range(nlat_out):
-
-                # get relevant entries depending on the normalization mode
-                if basis_norm_mode == "individual":
-                    iidx = torch.argwhere((idx[0] == ik) & (idx[1] == ilat))
-                    # normalize
-                    vnorm = torch.sum(psi_vals[iidx].abs() * q[iidx])
-                elif basis_norm_mode == "sum":
-                    # this will perform repeated normalization in the kernel dimension but this shouldn't lead to issues
-                    iidx = torch.argwhere(idx[1] == ilat)
-                    # normalize
-                    vnorm = torch.sum(psi_vals[iidx].abs() * q[iidx])
-                else:
-                    raise ValueError(f"Unknown basis normalization mode {basis_norm_mode}.")
-
-                if merge_quadrature:
-                    psi_vals[iidx] = psi_vals[iidx] * q[iidx] / (vnorm + eps)
-                else:
-                    psi_vals[iidx] = psi_vals[iidx] / (vnorm + eps)
+        ilat_out = idx[1]
+        ilat_in = idx[2]
+        nlat_out = out_shape[0]
+
+    # get the quadrature weights
+    q = quad_weights[ilat_in].reshape(-1)
+
+    # buffer to store intermediate values
+    vnorm = torch.zeros(kernel_size, nlat_out)
+
+    # loop through dimensions to compute the norms
+    for ik in range(kernel_size):
+        for ilat in range(nlat_out):
+
+            # find indices corresponding to the given output latitude and kernel basis function
+            iidx = torch.argwhere((ikernel == ik) & (ilat_out == ilat))
+
+            # compute the 2-norm, accounting for the fact that it is 4-pi normalized
+            vnorm[ik, ilat] = torch.sqrt(torch.sum(psi_vals[iidx].abs().pow(2) * q[iidx]) / 4 / torch.pi)
+
+    # loop over values and renormalize
+    for ik in range(kernel_size):
+        for ilat in range(nlat_out):
+
+            iidx = torch.argwhere((ikernel == ik) & (ilat_out == ilat))
+
+            if basis_norm_mode == "individual":
+                val = vnorm[ik, ilat]
+            elif basis_norm_mode == "mean":
+                val = vnorm[ik, :].mean()
+            elif basis_norm_mode == "none":
+                val = 1.0
+            else:
+                raise ValueError(f"Unknown basis normalization mode {basis_norm_mode}.")
+
+            if merge_quadrature:
+                psi_vals[iidx] = psi_vals[iidx] * q[iidx] / (val + eps)
+            else:
+                psi_vals[iidx] = psi_vals[iidx] / (val + eps)
+
+
+    if transpose_normalization and merge_quadrature:
+        psi_vals = psi_vals / correction_factor
 
     return psi_vals
 
@@ -133,7 +134,7 @@ def _precompute_convolution_tensor_s2(
     grid_out="equiangular",
     theta_cutoff=0.01 * math.pi,
     transpose_normalization=False,
-    basis_norm_mode="sum",
+    basis_norm_mode="none",
     merge_quadrature=False,
 ):
     """
@@ -187,11 +188,11 @@ def _precompute_convolution_tensor_s2(
         # compute cartesian coordinates of the rotated position
         # This uses the YZY convention of Euler angles, where the last angle (alpha) is a passive rotation,
         # and therefore applied with a negative sign
-        z = -torch.cos(beta) * torch.sin(alpha) * torch.sin(gamma) + torch.cos(alpha) * torch.cos(gamma)
         x = torch.cos(alpha) * torch.cos(beta) * torch.sin(gamma) + torch.cos(gamma) * torch.sin(alpha)
         y = torch.sin(beta) * torch.sin(gamma)
+        z = -torch.cos(beta) * torch.sin(alpha) * torch.sin(gamma) + torch.cos(alpha) * torch.cos(gamma)
 
-        # normalization is emportant to avoid NaNs when arccos and atan are applied
+        # normalization is important to avoid NaNs when arccos and atan are applied
         # this can otherwise lead to spurious artifacts in the solution
         norm = torch.sqrt(x * x + y * y + z * z)
         x = x / norm
@@ -200,7 +201,8 @@ def _precompute_convolution_tensor_s2(
 
         # compute spherical coordinates, where phi needs to fall into the [0, 2pi) range
         theta = torch.arccos(z)
-        phi = torch.arctan2(y, x) + torch.pi
+        phi = torch.arctan2(y, x)
+        phi = torch.where(phi < 0.0, phi + 2 * torch.pi, phi)
 
         # find the indices where the rotated position falls into the support of the kernel
         iidx, vals = filter_basis.compute_support_vals(theta, phi, r_cutoff=theta_cutoff)
@@ -293,7 +295,7 @@ class DiscreteContinuousConvS2(DiscreteContinuousConv):
         out_shape: Tuple[int],
         kernel_shape: Union[int, List[int]],
         basis_type: Optional[str] = "piecewise linear",
-        basis_norm_mode: Optional[str] = "sum",
+        basis_norm_mode: Optional[str] = "none",
         groups: Optional[int] = 1,
         grid_in: Optional[str] = "equiangular",
         grid_out: Optional[str] = "equiangular",
@@ -305,6 +307,9 @@ class DiscreteContinuousConvS2(DiscreteContinuousConv):
         self.nlat_in, self.nlon_in = in_shape
         self.nlat_out, self.nlon_out = out_shape
 
+        # make sure the p-shift works by checking that longitudes are divisible
+        assert self.nlon_in % self.nlon_out == 0
+
         # heuristic to compute theta cutoff based on the bandlimit of the input field and overlaps of the basis functions
         if theta_cutoff is None:
             theta_cutoff = torch.pi / float(self.nlat_out - 1)
@@ -396,7 +401,7 @@ class DiscreteContinuousConvTransposeS2(DiscreteContinuousConv):
         out_shape: Tuple[int],
         kernel_shape: Union[int, List[int]],
         basis_type: Optional[str] = "piecewise linear",
-        basis_norm_mode: Optional[str] = "sum",
+        basis_norm_mode: Optional[str] = "none",
         groups: Optional[int] = 1,
         grid_in: Optional[str] = "equiangular",
         grid_out: Optional[str] = "equiangular",
@@ -408,6 +413,9 @@ class DiscreteContinuousConvTransposeS2(DiscreteContinuousConv):
         self.nlat_in, self.nlon_in = in_shape
         self.nlat_out, self.nlon_out = out_shape
 
+        # make sure the p-shift works by checking that longitudes are divisible
+        assert self.nlon_out % self.nlon_in == 0
+
         # bandlimit
         if theta_cutoff is None:
             theta_cutoff = torch.pi / float(self.nlat_in - 1)
@@ -415,7 +423,7 @@ class DiscreteContinuousConvTransposeS2(DiscreteContinuousConv):
         if theta_cutoff <= 0.0:
             raise ValueError("Error, theta_cutoff has to be positive.")
 
-        # switch in_shape and out_shape since we want transpose conv
+        # switch in_shape and out_shape since we want the transpose convolution
         idx, vals = _precompute_convolution_tensor_s2(
             out_shape,
             in_shape,

torch_harmonics/distributed/distributed_convolution.py

@@ -76,7 +76,7 @@ def _precompute_distributed_convolution_tensor_s2(
     grid_out="equiangular",
     theta_cutoff=0.01 * math.pi,
     transpose_normalization=False,
-    basis_norm_mode="sum",
+    basis_norm_mode="none",
     merge_quadrature=False,
 ):
     """
@@ -142,7 +142,8 @@ def _precompute_distributed_convolution_tensor_s2(
 
         # compute spherical coordinates, where phi needs to fall into the [0, 2pi) range
         theta = torch.arccos(z)
-        phi = torch.arctan2(y, x) + torch.pi
+        phi = torch.arctan2(y, x)
+        phi = torch.where(phi < 0.0, phi + 2 * torch.pi, phi)
 
         # find the indices where the rotated position falls into the support of the kernel
         iidx, vals = filter_basis.compute_support_vals(theta, phi, r_cutoff=theta_cutoff)
@@ -207,7 +208,7 @@ class DistributedDiscreteContinuousConvS2(DiscreteContinuousConv):
         out_shape: Tuple[int],
         kernel_shape: Union[int, List[int]],
         basis_type: Optional[str] = "piecewise linear",
-        basis_norm_mode: Optional[str] = "sum",
+        basis_norm_mode: Optional[str] = "none",
         groups: Optional[int] = 1,
         grid_in: Optional[str] = "equiangular",
         grid_out: Optional[str] = "equiangular",
@@ -347,7 +348,7 @@ class DistributedDiscreteContinuousConvTransposeS2(DiscreteContinuousConv):
         out_shape: Tuple[int],
         kernel_shape: Union[int, List[int]],
         basis_type: Optional[str] = "piecewise linear",
-        basis_norm_mode: Optional[str] = "sum",
+        basis_norm_mode: Optional[str] = "none",
         groups: Optional[int] = 1,
         grid_in: Optional[str] = "equiangular",
         grid_out: Optional[str] = "equiangular",

torch_harmonics/filter_basis.py

@@ -41,12 +41,19 @@ def get_filter_basis(kernel_shape: Union[int, List[int], Tuple[int, int]], basis
 
     if basis_type == "piecewise linear":
         return PiecewiseLinearFilterBasis(kernel_shape=kernel_shape)
-    elif basis_type == "disk morlet":
-        return DiskMorletFilterBasis(kernel_shape=kernel_shape)
+    elif basis_type == "morlet":
+        return MorletFilterBasis(kernel_shape=kernel_shape)
+    elif basis_type == "zernike":
+        raise NotImplementedError()
     else:
         raise ValueError(f"Unknown basis_type {basis_type}")
 
 
+def _circle_dist(x1: torch.Tensor, x2: torch.Tensor):
+    """Helper function to compute the distance on a circle"""
+    return torch.minimum(torch.abs(x1 - x2), torch.abs(2 * math.pi - torch.abs(x1 - x2)))
+
+
 class FilterBasis(metaclass=abc.ABCMeta):
     """
     Abstract base class for a filter basis
@@ -64,6 +71,13 @@ class FilterBasis(metaclass=abc.ABCMeta):
     def kernel_size(self):
         raise NotImplementedError
 
+    # @abc.abstractmethod
+    # def compute_vals(self, r: torch.Tensor, phi: torch.Tensor, r_cutoff: float):
+    #     """
+    #     Computes the values of the filter basis
+    #     """
+    #     raise NotImplementedError
+
     @abc.abstractmethod
     def compute_support_vals(self, r: torch.Tensor, phi: torch.Tensor, r_cutoff: float):
         """
@@ -136,49 +150,49 @@ class PiecewiseLinearFilterBasis(FilterBasis):
         # disambiguate even and uneven cases and compute the support
         if nr % 2 == 1:
             ir = ((ikernel - 1) // nphi + 1) * dr
-            iphi = ((ikernel - 1) % nphi) * dphi
+            iphi = ((ikernel - 1) % nphi) * dphi - math.pi
         else:
             ir = (ikernel // nphi + 0.5) * dr
-            iphi = (ikernel % nphi) * dphi
+            iphi = (ikernel % nphi) * dphi - math.pi
 
         # find the indices where the rotated position falls into the support of the kernel
         if nr % 2 == 1:
             # find the support
             cond_r = ((r - ir).abs() <= dr) & (r <= r_cutoff)
-            cond_phi = (ikernel == 0) | ((phi - iphi).abs() <= dphi) | ((2 * math.pi - (phi - iphi).abs()) <= dphi)
+            cond_phi = (ikernel == 0) | (_circle_dist(phi, iphi).abs() <= dphi)
             # find indices where conditions are met
             iidx = torch.argwhere(cond_r & cond_phi)
             # compute the distance to the collocation points
             dist_r = (r[iidx[:, 1], iidx[:, 2]] - ir[iidx[:, 0], 0, 0]).abs()
-            dist_phi = (phi[iidx[:, 1], iidx[:, 2]] - iphi[iidx[:, 0], 0, 0]).abs()
+            dist_phi = _circle_dist(phi[iidx[:, 1], iidx[:, 2]], iphi[iidx[:, 0], 0, 0])
             # compute the value of the basis functions
             vals = 1 - dist_r / dr
             vals *= torch.where(
                 (iidx[:, 0] > 0),
-                (1 - torch.minimum(dist_phi, (2 * math.pi - dist_phi)) / dphi),
+                (1 - dist_phi / dphi),
                 1.0,
             )
 
         else:
-            # in the even case, the inner casis functions overlap into areas with a negative areas
+            # in the even case, the inner basis functions overlap into areas with a negative areas
             rn = -r
-            phin = torch.where(phi + math.pi >= 2 * math.pi, phi - math.pi, phi + math.pi)
+            phin = torch.where(phi + math.pi >= math.pi, phi - math.pi, phi + math.pi)
             # find the support
             cond_r = ((r - ir).abs() <= dr) & (r <= r_cutoff)
-            cond_phi = ((phi - iphi).abs() <= dphi) | ((2 * math.pi - (phi - iphi).abs()) <= dphi)
+            cond_phi = _circle_dist(phi, iphi).abs() <= dphi
             cond_rn = ((rn - ir).abs() <= dr) & (rn <= r_cutoff)
-            cond_phin = ((phin - iphi).abs() <= dphi) | ((2 * math.pi - (phin - iphi).abs()) <= dphi)
+            cond_phin = _circle_dist(phin, iphi) <= dphi
             # find indices where conditions are met
             iidx = torch.argwhere((cond_r & cond_phi) | (cond_rn & cond_phin))
             dist_r = (r[iidx[:, 1], iidx[:, 2]] - ir[iidx[:, 0], 0, 0]).abs()
-            dist_phi = (phi[iidx[:, 1], iidx[:, 2]] - iphi[iidx[:, 0], 0, 0]).abs()
+            dist_phi = _circle_dist(phi[iidx[:, 1], iidx[:, 2]], iphi[iidx[:, 0], 0, 0])
             dist_rn = (rn[iidx[:, 1], iidx[:, 2]] - ir[iidx[:, 0], 0, 0]).abs()
-            dist_phin = (phin[iidx[:, 1], iidx[:, 2]] - iphi[iidx[:, 0], 0, 0]).abs()
+            dist_phin = _circle_dist(phin[iidx[:, 1], iidx[:, 2]], iphi[iidx[:, 0], 0, 0])
             # compute the value of the basis functions
             vals = cond_r[iidx[:, 0], iidx[:, 1], iidx[:, 2]] * (1 - dist_r / dr)
-            vals *= cond_phi[iidx[:, 0], iidx[:, 1], iidx[:, 2]] * (1 - torch.minimum(dist_phi, (2 * math.pi - dist_phi)) / dphi)
+            vals *= cond_phi[iidx[:, 0], iidx[:, 1], iidx[:, 2]] * (1 - dist_phi / dphi)
             valsn = cond_rn[iidx[:, 0], iidx[:, 1], iidx[:, 2]] * (1 - dist_rn / dr)
-            valsn *= cond_phin[iidx[:, 0], iidx[:, 1], iidx[:, 2]] * (1 - torch.minimum(dist_phin, (2 * math.pi - dist_phin)) / dphi)
+            valsn *= cond_phin[iidx[:, 0], iidx[:, 1], iidx[:, 2]] * (1 - dist_phin / dphi)
             vals += valsn
 
         return iidx, vals
@@ -190,9 +204,10 @@ class PiecewiseLinearFilterBasis(FilterBasis):
         else:
             return self._compute_support_vals_isotropic(r, phi, r_cutoff=r_cutoff)
 
-class DiskMorletFilterBasis(FilterBasis):
+
+class MorletFilterBasis(FilterBasis):
     """
-    Morlet-like Filter basis. A Gaussian is multiplied with a Fourier basis in x and y.
+    Morlet-style filter basis on the disk. A Gaussian is multiplied with a Fourier basis in x and y directions
     """
 
     def __init__(
@@ -209,12 +224,12 @@ class DiskMorletFilterBasis(FilterBasis):
 
     @property
     def kernel_size(self):
-        return self.kernel_shape[0]*self.kernel_shape[1]
+        return self.kernel_shape[0] * self.kernel_shape[1]
 
-    def _gaussian_envelope(self, r: torch.Tensor, width: float =1.0):
-        return 1 / (2 * math.pi * width**2 ) * torch.exp(- 0.5 * r**2 / (width**2))
+    def _gaussian_window(self, r: torch.Tensor, width: float = 1.0):
+        return 1 / (2 * math.pi * width**2) * torch.exp(-0.5 * r**2 / (width**2))
 
-    def compute_support_vals(self, r: torch.Tensor, phi: torch.Tensor, r_cutoff: float):
+    def compute_support_vals(self, r: torch.Tensor, phi: torch.Tensor, r_cutoff: float, width: float = 0.25):
         """
         Computes the index set that falls into the isotropic kernel's support and returns both indices and values.
         """
@@ -227,26 +242,18 @@ class DiskMorletFilterBasis(FilterBasis):
         # get relevant indices
         iidx = torch.argwhere((r <= r_cutoff) & torch.full_like(ikernel, True, dtype=torch.bool))
 
-        # # computes the Gaussian envelope. To ensure that the curve is roughly 0 at the boundary, we rescale the Gaussian by 0.25
-        # width = 0.01
-        width = 0.25
-        # width = 1.0
-        # envelope = self._gaussian_envelope(r, width=0.25 * r_cutoff)
-
         # get x and y
         x = r * torch.sin(phi) / r_cutoff
         y = r * torch.cos(phi) / r_cutoff
 
-        harmonic = torch.where(nkernel % 2 == 1, torch.sin(torch.ceil(nkernel/2) * math.pi * x / width), torch.cos(torch.ceil(nkernel/2) * math.pi * x / width))
-        harmonic *= torch.where(mkernel % 2 == 1, torch.sin(torch.ceil(mkernel/2) * math.pi * y / width), torch.cos(torch.ceil(mkernel/2) * math.pi * y / width))
+        harmonic = torch.where(nkernel % 2 == 1, torch.sin(torch.ceil(nkernel / 2) * math.pi * x / width), torch.cos(torch.ceil(nkernel / 2) * math.pi * x / width))
+        harmonic *= torch.where(mkernel % 2 == 1, torch.sin(torch.ceil(mkernel / 2) * math.pi * y / width), torch.cos(torch.ceil(mkernel / 2) * math.pi * y / width))
 
         # disk area
         # disk_area = 2.0 * math.pi * (1.0 - math.cos(r_cutoff))
-        disk_area = 1
+        disk_area = 1.0
 
         # computes the Gaussian envelope. To ensure that the curve is roughly 0 at the boundary, we rescale the Gaussian by 0.25
-        vals = self._gaussian_envelope(r[iidx[:, 1], iidx[:, 2]] / r_cutoff, width=width) * harmonic[iidx[:, 0], iidx[:, 1], iidx[:, 2]] / disk_area
-        # vals = torch.ones_like(vals)
+        vals = self._gaussian_window(r[iidx[:, 1], iidx[:, 2]] / r_cutoff, width=width) * harmonic[iidx[:, 0], iidx[:, 1], iidx[:, 2]] / disk_area
 
         return iidx, vals
-

torch_harmonics/quadrature.py

@@ -2,7 +2,7 @@
 
 # SPDX-FileCopyrightText: Copyright (c) 2022 The torch-harmonics Authors. All rights reserved.
 # SPDX-License-Identifier: BSD-3-Clause
-# 
+#
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are met:
 #
@@ -31,6 +31,7 @@
 
 import numpy as np
 
+
 def _precompute_grid(n, grid="equidistant", a=0.0, b=1.0, periodic=False):
 
     if (grid != "equidistant") and periodic:
@@ -50,27 +51,31 @@ def _precompute_grid(n, grid="equidistant", a=0.0, b=1.0, periodic=False):
 
     return xlg, wlg
 
+
 def _precompute_latitudes(nlat, grid="equiangular"):
     r"""
     Convenience routine to precompute latitudes
     """
 
-    # compute coordinates
+    # compute coordinates in the cosine theta domain
     xlg, wlg = _precompute_grid(nlat, grid=grid, a=-1.0, b=1.0, periodic=False)
 
+    # to perform the quadrature and account for the jacobian of the sphere, the quadrature rule
+    # is formulated in the cosine theta domain, which is designed to integrate functions of cos theta
     lats = np.flip(np.arccos(xlg)).copy()
     wlg = np.flip(wlg).copy()
 
     return lats, wlg
 
+
 def trapezoidal_weights(n, a=-1.0, b=1.0, periodic=False):
     r"""
     Helper routine which returns equidistant nodes with trapezoidal weights
     on the interval [a, b]
     """
 
-    xlg = np.linspace(a, b, n)
-    wlg = (b - a) / (n - 1) * np.ones(n)
+    xlg = np.linspace(a, b, n, endpoint=periodic)
+    wlg = (b - a) / (n - periodic * 1) * np.ones(n)
 
     if not periodic:
         wlg[0] *= 0.5
@@ -78,6 +83,7 @@ def trapezoidal_weights(n, a=-1.0, b=1.0, periodic=False):
 
     return xlg, wlg
 
+
 def legendre_gauss_weights(n, a=-1.0, b=1.0):
     r"""
     Helper routine which returns the Legendre-Gauss nodes and weights
@@ -90,6 +96,7 @@ def legendre_gauss_weights(n, a=-1.0, b=1.0):
 
     return xlg, wlg
 
+
 def lobatto_weights(n, a=-1.0, b=1.0, tol=1e-16, maxiter=100):
     r"""
     Helper routine which returns the Legendre-Gauss-Lobatto nodes and weights
@@ -102,33 +109,33 @@ def lobatto_weights(n, a=-1.0, b=1.0, tol=1e-16, maxiter=100):
 
     # Vandermonde Matrix
     vdm = np.zeros((n, n))
-  
+
     # initialize Chebyshev nodes as first guess
-    for i in range(n): 
-        tlg[i] = -np.cos(np.pi*i / (n-1))
-    
+    for i in range(n):
+        tlg[i] = -np.cos(np.pi * i / (n - 1))
+
     tmp = 2.0
-    
+
     for i in range(maxiter):
         tmp = tlg
-       
-        vdm[:,0] = 1.0 
-        vdm[:,1] = tlg
-       
+
+        vdm[:, 0] = 1.0
+        vdm[:, 1] = tlg
+
         for k in range(2, n):
-            vdm[:, k] = ( (2*k-1) * tlg * vdm[:, k-1] - (k-1) * vdm[:, k-2] ) / k
-       
-        tlg = tmp - ( tlg*vdm[:, n-1] - vdm[:, n-2] ) / ( n * vdm[:, n-1]) 
-        
-        if (max(abs(tlg - tmp).flatten()) < tol ):
-            break 
-    
-    wlg = 2.0 / ( (n*(n-1))*(vdm[:, n-1]**2))
+            vdm[:, k] = ((2 * k - 1) * tlg * vdm[:, k - 1] - (k - 1) * vdm[:, k - 2]) / k
+
+        tlg = tmp - (tlg * vdm[:, n - 1] - vdm[:, n - 2]) / (n * vdm[:, n - 1])
+
+        if max(abs(tlg - tmp).flatten()) < tol:
+            break
+
+    wlg = 2.0 / ((n * (n - 1)) * (vdm[:, n - 1] ** 2))
 
     # rescale
     tlg = (b - a) * 0.5 * tlg + (b + a) * 0.5
     wlg = wlg * (b - a) * 0.5
-    
+
     return tlg, wlg
 
 
@@ -140,12 +147,12 @@ def clenshaw_curtiss_weights(n, a=-1.0, b=1.0):
     [1] Joerg Waldvogel, Fast Construction of the Fejer and Clenshaw-Curtis Quadrature Rules; BIT Numerical Mathematics, Vol. 43, No. 1, pp. 001–018.
     """
 
-    assert(n > 1)
+    assert n > 1
 
     tcc = np.cos(np.linspace(np.pi, 0, n))
 
     if n == 2:
-        wcc = np.array([1., 1.])
+        wcc = np.array([1.0, 1.0])
     else:
 
         n1 = n - 1
@@ -153,13 +160,13 @@ def clenshaw_curtiss_weights(n, a=-1.0, b=1.0):
         l = len(N)
         m = n1 - l
 
-        v = np.concatenate([2 / N / (N-2), 1 / N[-1:], np.zeros(m)])
+        v = np.concatenate([2 / N / (N - 2), 1 / N[-1:], np.zeros(m)])
         v = 0 - v[:-1] - v[-1:0:-1]
 
         g0 = -np.ones(n1)
         g0[l] = g0[l] + n1
         g0[m] = g0[m] + n1
-        g = g0 / (n1**2 - 1 + (n1%2))
+        g = g0 / (n1**2 - 1 + (n1 % 2))
         wcc = np.fft.ifft(v + g).real
         wcc = np.concatenate((wcc, wcc[:1]))
 
@@ -169,6 +176,7 @@ def clenshaw_curtiss_weights(n, a=-1.0, b=1.0):
 
     return tcc, wcc
 
+
 def fejer2_weights(n, a=-1.0, b=1.0):
     r"""
     Computation of the Fejer quadrature nodes and weights.
@@ -177,7 +185,7 @@ def fejer2_weights(n, a=-1.0, b=1.0):
     [1] Joerg Waldvogel, Fast Construction of the Fejer and Clenshaw-Curtis Quadrature Rules; BIT Numerical Mathematics, Vol. 43, No. 1, pp. 001–018.
     """
 
-    assert(n > 2)
+    assert n > 2
 
     tcc = np.cos(np.linspace(np.pi, 0, n))
 
@@ -186,7 +194,7 @@ def fejer2_weights(n, a=-1.0, b=1.0):
     l = len(N)
     m = n1 - l
 
-    v = np.concatenate([2 / N / (N-2), 1 / N[-1:], np.zeros(m)])
+    v = np.concatenate([2 / N / (N - 2), 1 / N[-1:], np.zeros(m)])
     v = 0 - v[:-1] - v[-1:0:-1]
 
     wcc = np.fft.ifft(v).real
@@ -196,4 +204,4 @@ def fejer2_weights(n, a=-1.0, b=1.0):
     tcc = (b - a) * 0.5 * tcc + (b + a) * 0.5
     wcc = wcc * (b - a) * 0.5
 
-    return tcc, wcc
\ No newline at end of file
+    return tcc, wcc

torch_harmonics/sht.py

@@ -68,19 +68,25 @@ class RealSHT(nn.Module):
 
         # TODO: include assertions regarding the dimensions
 
-        # compute quadrature points
+        # compute quadrature points and lmax based on the exactness of the quadrature
         if self.grid == "legendre-gauss":
             cost, w = legendre_gauss_weights(nlat, -1, 1)
+            # maximum polynomial degree for Gauss Legendre is 2 * nlat - 1 >= 2 * lmax
+            # and therefore lmax = nlat - 1 (inclusive)
             self.lmax = lmax or self.nlat
         elif self.grid == "lobatto":
             cost, w = lobatto_weights(nlat, -1, 1)
-            self.lmax = lmax or self.nlat-1
+            # maximum polynomial degree for Gauss Legendre is 2 * nlat - 3 >= 2 * lmax
+            # and therefore lmax = nlat - 2 (inclusive)
+            self.lmax = lmax or self.nlat - 1
         elif self.grid == "equiangular":
             cost, w = clenshaw_curtiss_weights(nlat, -1, 1)
-            # cost, w = fejer2_weights(nlat, -1, 1)
+            # in principle, Clenshaw-Curtiss quadrature is only exact up to polynomial degrees of nlat
+            # however, we observe that the quadrature is remarkably accurate for higher degress. This is why we do not
+            # choose a lower lmax for now.
             self.lmax = lmax or self.nlat
         else:
-            raise(ValueError("Unknown quadrature mode"))
+            raise (ValueError("Unknown quadrature mode"))
 
         # apply cosine transform and flip them
         tq = np.flip(np.arccos(cost))
@@ -92,24 +98,24 @@ class RealSHT(nn.Module):
         weights = torch.from_numpy(w)
         pct = _precompute_legpoly(self.mmax, self.lmax, tq, norm=self.norm, csphase=self.csphase)
         pct = torch.from_numpy(pct)
-        weights = torch.einsum('mlk,k->mlk', pct, weights)
+        weights = torch.einsum("mlk,k->mlk", pct, weights)
 
         # remember quadrature weights
-        self.register_buffer('weights', weights, persistent=False)
+        self.register_buffer("weights", weights, persistent=False)
 
     def extra_repr(self):
         r"""
         Pretty print module
         """
-        return f'nlat={self.nlat}, nlon={self.nlon},\n lmax={self.lmax}, mmax={self.mmax},\n grid={self.grid}, csphase={self.csphase}'
+        return f"nlat={self.nlat}, nlon={self.nlon},\n lmax={self.lmax}, mmax={self.mmax},\n grid={self.grid}, csphase={self.csphase}"
 
     def forward(self, x: torch.Tensor):
 
         if x.dim() < 2:
             raise ValueError(f"Expected tensor with at least 2 dimensions but got {x.dim()} instead")
 
-        assert(x.shape[-2] == self.nlat)
-        assert(x.shape[-1] == self.nlon)
+        assert x.shape[-2] == self.nlat
+        assert x.shape[-1] == self.nlon
 
         # apply real fft in the longitudinal direction
         x = 2.0 * torch.pi * torch.fft.rfft(x, dim=-1, norm="forward")
@@ -124,12 +130,13 @@ class RealSHT(nn.Module):
         xout = torch.zeros(out_shape, dtype=x.dtype, device=x.device)
 
         # contraction
-        xout[..., 0] = torch.einsum('...km,mlk->...lm', x[..., :self.mmax, 0], self.weights.to(x.dtype) )
-        xout[..., 1] = torch.einsum('...km,mlk->...lm', x[..., :self.mmax, 1], self.weights.to(x.dtype) )
+        xout[..., 0] = torch.einsum("...km,mlk->...lm", x[..., : self.mmax, 0], self.weights.to(x.dtype))
+        xout[..., 1] = torch.einsum("...km,mlk->...lm", x[..., : self.mmax, 1], self.weights.to(x.dtype))
         x = torch.view_as_complex(xout)
 
         return x
 
+
 class InverseRealSHT(nn.Module):
     r"""
     Defines a module for computing the inverse (real-valued) SHT.
@@ -157,12 +164,12 @@ class InverseRealSHT(nn.Module):
             self.lmax = lmax or self.nlat
         elif self.grid == "lobatto":
             cost, _ = lobatto_weights(nlat, -1, 1)
-            self.lmax = lmax or self.nlat-1
+            self.lmax = lmax or self.nlat - 1
         elif self.grid == "equiangular":
             cost, _ = clenshaw_curtiss_weights(nlat, -1, 1)
             self.lmax = lmax or self.nlat
         else:
-            raise(ValueError("Unknown quadrature mode"))
+            raise (ValueError("Unknown quadrature mode"))
 
         # apply cosine transform and flip them
         t = np.flip(np.arccos(cost))
@@ -174,27 +181,27 @@ class InverseRealSHT(nn.Module):
         pct = torch.from_numpy(pct)
 
         # register buffer
-        self.register_buffer('pct', pct, persistent=False)
+        self.register_buffer("pct", pct, persistent=False)
 
     def extra_repr(self):
         r"""
         Pretty print module
         """
-        return f'nlat={self.nlat}, nlon={self.nlon},\n lmax={self.lmax}, mmax={self.mmax},\n grid={self.grid}, csphase={self.csphase}'
+        return f"nlat={self.nlat}, nlon={self.nlon},\n lmax={self.lmax}, mmax={self.mmax},\n grid={self.grid}, csphase={self.csphase}"
 
     def forward(self, x: torch.Tensor):
 
         if len(x.shape) < 2:
             raise ValueError(f"Expected tensor with at least 2 dimensions but got {len(x.shape)} instead")
 
-        assert(x.shape[-2] == self.lmax)
-        assert(x.shape[-1] == self.mmax)
+        assert x.shape[-2] == self.lmax
+        assert x.shape[-1] == self.mmax
 
         # Evaluate associated Legendre functions on the output nodes
         x = torch.view_as_real(x)
 
-        rl = torch.einsum('...lm, mlk->...km', x[..., 0], self.pct.to(x.dtype) )
-        im = torch.einsum('...lm, mlk->...km', x[..., 1], self.pct.to(x.dtype) )
+        rl = torch.einsum("...lm, mlk->...km", x[..., 0], self.pct.to(x.dtype))
+        im = torch.einsum("...lm, mlk->...km", x[..., 1], self.pct.to(x.dtype))
         xs = torch.stack((rl, im), -1)
 
         # apply the inverse (real) FFT
@@ -238,13 +245,12 @@ class RealVectorSHT(nn.Module):
             self.lmax = lmax or self.nlat
         elif self.grid == "lobatto":
             cost, w = lobatto_weights(nlat, -1, 1)
-            self.lmax = lmax or self.nlat-1
+            self.lmax = lmax or self.nlat - 1
         elif self.grid == "equiangular":
             cost, w = clenshaw_curtiss_weights(nlat, -1, 1)
-            # cost, w = fejer2_weights(nlat, -1, 1)
             self.lmax = lmax or self.nlat
         else:
-            raise(ValueError("Unknown quadrature mode"))
+            raise (ValueError("Unknown quadrature mode"))
 
         # apply cosine transform and flip them
         tq = np.flip(np.arccos(cost))
@@ -258,28 +264,28 @@ class RealVectorSHT(nn.Module):
 
         # combine integration weights, normalization factor in to one:
         l = torch.arange(0, self.lmax)
-        norm_factor = 1. / l / (l+1)
-        norm_factor[0] = 1.
-        weights = torch.einsum('dmlk,k,l->dmlk', dpct, weights, norm_factor)
+        norm_factor = 1.0 / l / (l + 1)
+        norm_factor[0] = 1.0
+        weights = torch.einsum("dmlk,k,l->dmlk", dpct, weights, norm_factor)
         # since the second component is imaginary, we need to take complex conjugation into account
         weights[1] = -1 * weights[1]
 
         # remember quadrature weights
-        self.register_buffer('weights', weights, persistent=False)
+        self.register_buffer("weights", weights, persistent=False)
 
     def extra_repr(self):
         r"""
         Pretty print module
         """
-        return f'nlat={self.nlat}, nlon={self.nlon},\n lmax={self.lmax}, mmax={self.mmax},\n grid={self.grid}, csphase={self.csphase}'
+        return f"nlat={self.nlat}, nlon={self.nlon},\n lmax={self.lmax}, mmax={self.mmax},\n grid={self.grid}, csphase={self.csphase}"
 
     def forward(self, x: torch.Tensor):
 
         if x.dim() < 3:
             raise ValueError(f"Expected tensor with at least 3 dimensions but got {x.dim()} instead")
 
-        assert(x.shape[-2] == self.nlat)
-        assert(x.shape[-1] == self.nlon)
+        assert x.shape[-2] == self.nlat
+        assert x.shape[-1] == self.nlon
 
         # apply real fft in the longitudinal direction
         x = 2.0 * torch.pi * torch.fft.rfft(x, dim=-1, norm="forward")
@@ -295,20 +301,24 @@ class RealVectorSHT(nn.Module):
 
         # contraction - spheroidal component
         # real component
-        xout[..., 0, :, :, 0] =   torch.einsum('...km,mlk->...lm', x[..., 0, :, :self.mmax, 0], self.weights[0].to(x.dtype)) \
-                                - torch.einsum('...km,mlk->...lm', x[..., 1, :, :self.mmax, 1], self.weights[1].to(x.dtype))
+        xout[..., 0, :, :, 0] = torch.einsum("...km,mlk->...lm", x[..., 0, :, : self.mmax, 0], self.weights[0].to(x.dtype)) - torch.einsum(
+            "...km,mlk->...lm", x[..., 1, :, : self.mmax, 1], self.weights[1].to(x.dtype)
+        )
 
         # iamg component
-        xout[..., 0, :, :, 1] =   torch.einsum('...km,mlk->...lm', x[..., 0, :, :self.mmax, 1], self.weights[0].to(x.dtype)) \
-                                + torch.einsum('...km,mlk->...lm', x[..., 1, :, :self.mmax, 0], self.weights[1].to(x.dtype))
+        xout[..., 0, :, :, 1] = torch.einsum("...km,mlk->...lm", x[..., 0, :, : self.mmax, 1], self.weights[0].to(x.dtype)) + torch.einsum(
+            "...km,mlk->...lm", x[..., 1, :, : self.mmax, 0], self.weights[1].to(x.dtype)
+        )
 
         # contraction - toroidal component
         # real component
-        xout[..., 1, :, :, 0] = - torch.einsum('...km,mlk->...lm', x[..., 0, :, :self.mmax, 1], self.weights[1].to(x.dtype)) \
-                                - torch.einsum('...km,mlk->...lm', x[..., 1, :, :self.mmax, 0], self.weights[0].to(x.dtype))
+        xout[..., 1, :, :, 0] = -torch.einsum("...km,mlk->...lm", x[..., 0, :, : self.mmax, 1], self.weights[1].to(x.dtype)) - torch.einsum(
+            "...km,mlk->...lm", x[..., 1, :, : self.mmax, 0], self.weights[0].to(x.dtype)
+        )
         # imag component
-        xout[..., 1, :, :, 1] =   torch.einsum('...km,mlk->...lm', x[..., 0, :, :self.mmax, 0], self.weights[1].to(x.dtype)) \
-                                - torch.einsum('...km,mlk->...lm', x[..., 1, :, :self.mmax, 1], self.weights[0].to(x.dtype))
+        xout[..., 1, :, :, 1] = torch.einsum("...km,mlk->...lm", x[..., 0, :, : self.mmax, 0], self.weights[1].to(x.dtype)) - torch.einsum(
+            "...km,mlk->...lm", x[..., 1, :, : self.mmax, 1], self.weights[0].to(x.dtype)
+        )
 
         return torch.view_as_complex(xout)
 
@@ -321,6 +331,7 @@ class InverseRealVectorSHT(nn.Module):
     [1] Schaeffer, N. Efficient spherical harmonic transforms aimed at pseudospectral numerical simulations, G3: Geochemistry, Geophysics, Geosystems.
     [2] Wang, B., Wang, L., Xie, Z.; Accurate calculation of spherical and vector spherical harmonic expansions via spectral element grids; Adv Comput Math.
     """
+
     def __init__(self, nlat, nlon, lmax=None, mmax=None, grid="equiangular", norm="ortho", csphase=True):
 
         super().__init__()
@@ -337,12 +348,12 @@ class InverseRealVectorSHT(nn.Module):
             self.lmax = lmax or self.nlat
         elif self.grid == "lobatto":
             cost, _ = lobatto_weights(nlat, -1, 1)
-            self.lmax = lmax or self.nlat-1
+            self.lmax = lmax or self.nlat - 1
         elif self.grid == "equiangular":
             cost, _ = clenshaw_curtiss_weights(nlat, -1, 1)
             self.lmax = lmax or self.nlat
         else:
-            raise(ValueError("Unknown quadrature mode"))
+            raise (ValueError("Unknown quadrature mode"))
 
         # apply cosine transform and flip them
         t = np.flip(np.arccos(cost))
@@ -354,40 +365,36 @@ class InverseRealVectorSHT(nn.Module):
         dpct = torch.from_numpy(dpct)
 
         # register weights
-        self.register_buffer('dpct', dpct, persistent=False)
+        self.register_buffer("dpct", dpct, persistent=False)
 
     def extra_repr(self):
         r"""
         Pretty print module
         """
-        return f'nlat={self.nlat}, nlon={self.nlon},\n lmax={self.lmax}, mmax={self.mmax},\n grid={self.grid}, csphase={self.csphase}'
+        return f"nlat={self.nlat}, nlon={self.nlon},\n lmax={self.lmax}, mmax={self.mmax},\n grid={self.grid}, csphase={self.csphase}"
 
     def forward(self, x: torch.Tensor):
 
         if x.dim() < 3:
             raise ValueError(f"Expected tensor with at least 3 dimensions but got {x.dim()} instead")
 
-        assert(x.shape[-2] == self.lmax)
-        assert(x.shape[-1] == self.mmax)
+        assert x.shape[-2] == self.lmax
+        assert x.shape[-1] == self.mmax
 
         # Evaluate associated Legendre functions on the output nodes
         x = torch.view_as_real(x)
 
         # contraction - spheroidal component
         # real component
-        srl =   torch.einsum('...lm,mlk->...km', x[..., 0, :, :, 0], self.dpct[0].to(x.dtype)) \
-              - torch.einsum('...lm,mlk->...km', x[..., 1, :, :, 1], self.dpct[1].to(x.dtype))
+        srl = torch.einsum("...lm,mlk->...km", x[..., 0, :, :, 0], self.dpct[0].to(x.dtype)) - torch.einsum("...lm,mlk->...km", x[..., 1, :, :, 1], self.dpct[1].to(x.dtype))
         # iamg component
-        sim =   torch.einsum('...lm,mlk->...km', x[..., 0, :, :, 1], self.dpct[0].to(x.dtype)) \
-              + torch.einsum('...lm,mlk->...km', x[..., 1, :, :, 0], self.dpct[1].to(x.dtype))
+        sim = torch.einsum("...lm,mlk->...km", x[..., 0, :, :, 1], self.dpct[0].to(x.dtype)) + torch.einsum("...lm,mlk->...km", x[..., 1, :, :, 0], self.dpct[1].to(x.dtype))
 
         # contraction - toroidal component
         # real component
-        trl = - torch.einsum('...lm,mlk->...km', x[..., 0, :, :, 1], self.dpct[1].to(x.dtype)) \
-              - torch.einsum('...lm,mlk->...km', x[..., 1, :, :, 0], self.dpct[0].to(x.dtype))
+        trl = -torch.einsum("...lm,mlk->...km", x[..., 0, :, :, 1], self.dpct[1].to(x.dtype)) - torch.einsum("...lm,mlk->...km", x[..., 1, :, :, 0], self.dpct[0].to(x.dtype))
         # imag component
-        tim =   torch.einsum('...lm,mlk->...km', x[..., 0, :, :, 0], self.dpct[1].to(x.dtype)) \
-              - torch.einsum('...lm,mlk->...km', x[..., 1, :, :, 1], self.dpct[0].to(x.dtype))
+        tim = torch.einsum("...lm,mlk->...km", x[..., 0, :, :, 0], self.dpct[1].to(x.dtype)) - torch.einsum("...lm,mlk->...km", x[..., 1, :, :, 1], self.dpct[0].to(x.dtype))
 
         # reassemble
         s = torch.stack((srl, sim), -1)