Rewrite AuraFlowPatchEmbed.pe_selection_index_based_on_dim to be torch.compile compatible (#11297)

* Update pe_selection_index_based_on_dim

* Make pe_selection_index_based_on_dim work with torh.compile

* Fix AuraFlowTransformer2DModel's dpcstring default values

---------
Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>

src/diffusers/models/transformers/auraflow_transformer_2d.py

@@ -74,15 +74,23 @@ class AuraFlowPatchEmbed(nn.Module):
         # PE will be viewed as 2d-grid, and H/p x W/p of the PE will be selected
         # because original input are in flattened format, we have to flatten this 2d grid as well.
         h_p, w_p = h // self.patch_size, w // self.patch_size
-        original_pe_indexes = torch.arange(self.pos_embed.shape[1])
         h_max, w_max = int(self.pos_embed_max_size**0.5), int(self.pos_embed_max_size**0.5)
-        original_pe_indexes = original_pe_indexes.view(h_max, w_max)
+
+        # Calculate the top-left corner indices for the centered patch grid
         starth = h_max // 2 - h_p // 2
-        endh = starth + h_p
         startw = w_max // 2 - w_p // 2
-        endw = startw + w_p
-        original_pe_indexes = original_pe_indexes[starth:endh, startw:endw]
-        return original_pe_indexes.flatten()
+
+        # Generate the row and column indices for the desired patch grid
+        rows = torch.arange(starth, starth + h_p, device=self.pos_embed.device)
+        cols = torch.arange(startw, startw + w_p, device=self.pos_embed.device)
+
+        # Create a 2D grid of indices
+        row_indices, col_indices = torch.meshgrid(rows, cols, indexing="ij")
+
+        # Convert the 2D grid indices to flattened 1D indices
+        selected_indices = (row_indices * w_max + col_indices).flatten()
+
+        return selected_indices
 
     def forward(self, latent):
         batch_size, num_channels, height, width = latent.size()
@@ -275,17 +283,17 @@ class AuraFlowTransformer2DModel(ModelMixin, ConfigMixin, PeftAdapterMixin, From
         sample_size (`int`): The width of the latent images. This is fixed during training since
             it is used to learn a number of position embeddings.
         patch_size (`int`): Patch size to turn the input data into small patches.
-        in_channels (`int`, *optional*, defaults to 16): The number of channels in the input.
+        in_channels (`int`, *optional*, defaults to 4): The number of channels in the input.
         num_mmdit_layers (`int`, *optional*, defaults to 4): The number of layers of MMDiT Transformer blocks to use.
-        num_single_dit_layers (`int`, *optional*, defaults to 4):
+        num_single_dit_layers (`int`, *optional*, defaults to 32):
             The number of layers of Transformer blocks to use. These blocks use concatenated image and text
             representations.
-        attention_head_dim (`int`, *optional*, defaults to 64): The number of channels in each head.
-        num_attention_heads (`int`, *optional*, defaults to 18): The number of heads to use for multi-head attention.
+        attention_head_dim (`int`, *optional*, defaults to 256): The number of channels in each head.
+        num_attention_heads (`int`, *optional*, defaults to 12): The number of heads to use for multi-head attention.
         joint_attention_dim (`int`, *optional*): The number of `encoder_hidden_states` dimensions to use.
         caption_projection_dim (`int`): Number of dimensions to use when projecting the `encoder_hidden_states`.
-        out_channels (`int`, defaults to 16): Number of output channels.
-        pos_embed_max_size (`int`, defaults to 4096): Maximum positions to embed from the image latents.
+        out_channels (`int`, defaults to 4): Number of output channels.
+        pos_embed_max_size (`int`, defaults to 1024): Maximum positions to embed from the image latents.
     """
 
     _no_split_modules = ["AuraFlowJointTransformerBlock", "AuraFlowSingleTransformerBlock", "AuraFlowPatchEmbed"]