sub.py

from .add import scatter_add


def scatter_sub(src, index, dim=-1, out=None, dim_size=None, fill_value=0):
    r"""
    |

    .. image:: https://raw.githubusercontent.com/rusty1s/pytorch_scatter/
            master/docs/source/_figures/sub.svg?sanitize=true
        :align: center
        :width: 400px

    |

    Subtracts all values from the :attr:`src` tensor into :attr:`out` at the
    indices specified in the :attr:`index` tensor along an given axis
    :attr:`dim`.If multiple indices reference the same location, their
    **negated contributions add** (`cf.` :meth:`~torch_scatter.scatter_add`).

    For one-dimensional tensors, the operation computes

    .. math::
        \mathrm{out}_i = \mathrm{out}_i - \sum_j \mathrm{src}_j

    where :math:`\sum` is over :math:`j` such that
    :math:`\mathrm{index}_j = i`.

    Args:
        src (Tensor): The source tensor.
        index (LongTensor): The indices of elements to scatter.
        dim (int, optional): The axis along which to index.
            (default: :obj:`-1`)
        out (Tensor, optional): The destination tensor. (default: :obj:`None`)
        dim_size (int, optional): If :attr:`out` is not given, automatically
            create output with size :attr:`dim_size` at dimension :attr:`dim`.
            If :attr:`dim_size` is not given, a minimal sized output tensor is
            returned. (default: :obj:`None`)
        fill_value (int, optional): If :attr:`out` is not given, automatically
            fill output tensor with :attr:`fill_value`. (default: :obj:`0`)

    :rtype: :class:`Tensor`

    .. testsetup::

        import torch

    .. testcode::

        from torch_scatter import scatter_sub
        src = torch.tensor([[2, 0, 1, 4, 3], [0, 2, 1, 3, 4]])
        index = torch.tensor([[4, 5, 4, 2, 3], [0, 0, 2, 2, 1]])
        out = src.new_zeros((2, 6))
        out = scatter_sub(src, index, out=out)
        print(out)

    .. testoutput::

        0  0 -4 -3 -3  0
       -2 -4 -4  0  0  0
       [torch.FloatTensor of size 2x6]
    """
    return scatter_add(src.neg(), index, dim, out, dim_size, fill_value)