torch.sparse.addmm
torch.sparse.addmm(mat, mat1, mat2, *, beta=1., alpha=1.) -> Tensor
This function does exact same thing as "torch.addmm()" in the
   forward, except that it supports backward for sparse COO matrix
   "mat1". When "mat1" is a COO tensor it must have sparse_dim = 2.
   When inputs are COO tensors, this function also supports backward
   for both inputs.
Supports both CSR and COO storage formats.
Note:
 This function doesn't support computing derivaties with respect
 to CSR matrices.

Parameters:
      * mat (Tensor) -- a dense matrix to be added
  * **mat1** (*Tensor*) -- a sparse matrix to be multiplied

  * **mat2** (*Tensor*) -- a dense matrix to be multiplied

  * **beta** (*Number**, **optional*) -- multiplier for "mat"
    (\beta)

  * **alpha** (*Number**, **optional*) -- multiplier for mat1 @
    mat2 (\alpha)
