fix forward and backward for norm with negative infinity norm

[Separius]

I found a bug in norm() and fixed it (and added tests to make sure it's fixed)
here is how to reproduce it:

import torch
x = torch.FloatTensor([[10, 12, 13], [4, 0, 12]])
print(torch.norm(x, -40, dim=0, keepdim=True)) #output is tensor([[ 4.0000,  0.0000, 11.9853]])
print(torch.norm(x, float('-inf'), dim=0, keepdim=True)) #output is tensor([[1., 1., 1.]]) which is wrong!
from numpy.linalg import norm as np_norm
x = x.numpy()
print(np_norm(x, ord=-40, axis=0)) #output is array([[4., 0., 11.985261]])
print(np_norm(x, ord=float('-inf'), axis=0)) #output is array([[4., 0., 12.0]])

it's related to #6817 and #6969

[ssnl]

Nice! Code looks very reasonable. Thank you! Our CI seems to be having some problem. Could you rebase to master and force push? Sorry about it!

[Separius]

@ssnl I checked CI's log and there were two problems, one is with data_loader which is probably unrelated to my code, but the other one was a jit test that my code failed, turns out there is a function in test_jit.py named get_constants() and I think it has a bug(an obvious one), but maybe(0.001%) it was intentional, can you check that too?; I will rebase after that
one more thing is it better to squash all my commits into one or two is better in this case? (jit test; norm)

Edit: ah, looks like it was intentional :),
RuntimeError: Only 'inf' can be cast to a float, but got '-inf' (operator() at /var/lib/jenkins/workspace/torch/csrc/jit/register_prim_ops.cpp:178)
I can look at register_prim_ops.cpp and change it to accept -inf or I can simply exclude -inf test in jit
first one is obviously better, right?

Edit: I changed register_prim_ops.cpp to accept -inf too

[ssnl]

Oh Thanks! I must admit that I didn't look at the log and assumed that it's the CI base commit problem (rebase usually solves that). My bad! We recently switched from jenkins to CircleCI so there are still some rough edges around CI. Thanks for fixing the JIT issue!

[Separius]

rebased and squashed all commits into one, ready to merge! :) @ssnl
BTW: thanks for your fast replies

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ezyang is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[zou3519]

jit changes look good, but please add a test for -inf to

pytorch/test/test_jit.py

Lines 2811 to 2816 in 7edfe11

	def test_inf(self):
	@torch.jit.script
	def foo(a):
	return a < float('inf')
	s = torch.rand(1)
	self.assertTrue(foo(s))

[Separius]

@zou3519 fixed the error message and added a test for -inf

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soumith is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.