code: def ravel_index(idx, dims) -> torch.Tensor:
      """
      Computes the linear index in an array of shape dims.
      It performs the reverse functionality of unravel_index
      Args:
        idx: A LongTensor of shape (N, 3). Each row corresponds to indices into an
            array of dimensions dims.
        dims: The shape of the array to be indexed.
      Implemented only for dims=(H, W, D)
      """
      if len(dims) != 3:
          raise ValueError("Expects a 3-element list")
      if idx.shape[1] != 3:
          raise ValueError("Expects an index tensor of shape Nx3")
      H, W, D = dims
      linind = idx[:, 0] * W * D + idx[:, 1] * D + idx[:, 2]
      return linind
  
imports: import torch
  import torch.nn.functional
  from pytorch3d.common.compat import meshgrid_ij
  from pytorch3d.structures import Meshes
label_desc: Use image node_id 2 for calling a global function with example usage: ravel_index(idx, dims) and returns: linind