add.at-like addition using sparse matrices

example.py

import torch
indices = torch.LongTensor([[1,1,1],
                            [2,1,1]]) # must be two dimensional with one row per dimension
values = torch.arange(1,4)
size = torch.Size((3,3))
a = torch.sparse.FloatTensor(indices, values, size)
b = torch.eye(3)
b += a
print (b)