Add / substract between matrix and vector in pytorch

I want to do + / - / * between matrix and vector in pytorch.
How can I do with good performance?
I tried to use expand, but it's really slow (I am using big matrix with small vector).

a = torch.rand(2,3)
print(a)
0.7420 0.2990 0.3896
0.0715 0.6719 0.0602
[torch.FloatTensor of size 2x3]
b = torch.rand(2)
print(b)
0.3773
0.6757
[torch.FloatTensor of size 2]
a.add(b)
Traceback (most recent call last):
File "C:ProgramDataAnaconda3libsite-packagesIPythoncoreinteractiveshell.py", line 3066, in run_code
exec(code_obj, self.user_global_ns, self.user_ns)
File "<ipython-input-17-a1cb1b03d031>", line 1, in <module>
a.add(b)
RuntimeError: inconsistent tensor size, expected r_ [2 x 3], t [2 x 3] and src [2] to have the same number of elements, but got 6, 6 and 2 elements respectively at c:miniconda2conda-bldpytorch-cpu_1519449358620worktorchlibthgeneric/THTensorMath.c:1021


Expected result:

0.7420-0.3773 0.2990-0.3773 0.3896-0.3773
0.0715-0.6757 0.6719-0.6757 0.0602-0.6757


1 Answer
1

what about reshaping?

In [2]: a = torch.rand(2,3)
...:

In [3]: a
Out[3]:
tensor([[ 0.2207, 0.1203, 0.7908],
[ 0.6702, 0.7557, 0.0708]])

In [4]: b = torch.rand(2)
...:

In [5]: b
Out[5]: tensor([ 0.5953, 0.7925])

In [6]: a.add(b.reshape(-1,1))
Out[6]:
tensor([[ 0.8160, 0.7156, 1.3861],
[ 1.4627, 1.5481, 0.8632]])


also check about the broadcasting: https://pytorch.org/docs/stable/notes/broadcasting.html

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