A = torch.zeros(5, 4)
B = torch.arange(0, 9).view(3, 3)
C = torch.arange(0, 15).view(3, 5)
idxs = torch.LongTensor([0, 2, 4])

A.index_add_(0, idxs, B)
# RuntimeError: inconsistent tensor size, expected r_ [4], t [4] and src
  [3] to have the same number of elements, but got 4, 4 and 3 elements
  respectively at (...)/aten/src/TH/generic/THTensorMath.c:1008

A.index_add_(0, idxs, C)
# RuntimeError: inconsistent tensor size, expected r_ [4], t [4] and src
  [5] to have the same number of elements, but got 4, 4 and 5 elements
  respectively at (...)/aten/src/TH/generic/THTensorMath.c:1008

A = torch.zeros(5, 4).cuda()
B = torch.arange(0, 9).view(3, 3).cuda()
C = torch.arange(0, 15).view(3, 5).cuda()
idxs = torch.LongTensor([0, 2, 4]).cuda()

A.index_add_(0, idxs, B)
print(A)
#    0  1  2  0
#    0  0  0  0
#    3  4  5  0
#    0  0  0  0
#    6  7  8  0
#   [torch.cuda.FloatTensor of size 5x4 (GPU 0)]

A.zero_()
A.index_add_(0, idxs, C)
print(A)
#     0   1   2   3
#     4   0   0   0
#     5   6   7   8
#     9   0   0   0
#    10  11  12  13
#   [torch.cuda.FloatTensor of size 5x4 (GPU 0)]