>>> indices = torch.tensor([[1, 1, 2], [1, 2, 0]])
>>> val = torch.ones(len(row)).long()
>>> A = dglsp.spmatrix(indices, val, shape=(3, 4))
>>> A.float()
SparseMatrix(indices=tensor([[1, 1, 2],
[1, 2, 0]]),
values=tensor([1., 1., 1.]),
shape=(3, 4), nnz=3)