What is manual_seed?

1

hi, i saw this from a dcgan codes . it seems it relates to cuda
here are parts of the code

if opt.manualSeed is None:
opt.manualSeed = random.randint(1, 10000)
print("Random Seed: ", opt.manualSeed)
random.seed(opt.manualSeed)
torch.manual_seed(opt.manualSeed)
if opt.cuda:
torch.cuda.manual_seed_all(opt.manualSeed)

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2

manual_seed sets the random seed from pytorch random number generators, as explained in the docs.

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3

But I still cannot understand why there should exist such code. Where are these generated random numbers used? It seems that “opt.manualSeed” has never been called later on.

4

You just need to call torch.manual_seed(seed), and it will set the seed of the random number generator to a fixed value, so that when you call for example torch.rand(2), the results will be reproducible.
An example

import torch

torch.manual_seed(2)
print(torch.rand(2))

gives you

 0.4360
 0.1851
[torch.FloatTensor of size 2]

Try now without the torch.manual_seed, and you’ll see that it changes over time.

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5

Hey @fmassa, in the above codes, what’s the differences between random.seed(opt.manualSeed) and torch.manual_seed(opt.manualSeed)? It seems the both of the two are produce seeds. Are they repetitive? Thanks!

6

@Mylinda first one is for python RNG, second is for pytorch RNG

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7

Yes, I got this point. Can the codes use torch.manual_seed(opt.manualSeed) directly and merely? What is the significance of random.seed(opt.manualSeed)? Is it redundant? @smth

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8

depends on the code. if you are using python’s random package and any of it’s functions, you want to also do random.seed(...)

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9

Got it. Thanks @smth

10

where is opt.manualSeed coming from? how is it getting its number for seeding purposes?

11

It’s probably defined in the DCGAN example. In this line the arguments from the argparser are assigned to opt.

However, this is just an example code. You can use whatever number you like.

12

is it possible to use os.urandom(n) to seed pytorch?

Do:

ord(os.urandom(1))
13

For the record, manual_seed seeds all of pytorch:

http://pytorch.org/docs/master/torch.html?highlight=manual%20seed#torch.manual_seed

14

Hi
Does that means once we set manual_seed fixed, parameter in RandomResizedCrop , RandomRotation will be fixed in every iteration?

15

No.
The random values will be still “random” but in a defined order.
I.e. if you restart your script, the same random numbers will be created.
Have a look at PRNG for more information.

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16

Thus, to seed everything, on the assumption one is using PyTorch and Numpy:

# use_cuda = torch.cuda.is_available() 
# ...
def random_seeding(seed_value, use_cuda):
    numpy.random.seed(seed_value) # cpu vars
    torch.manual_seed(seed_value) # cpu  vars
    if use_cuda: torch.cuda.manual_seed_all(seed_value) # gpu vars

Anything else is missing?

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17

You should also seed the python random:

import random
random.seed(seed)
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18

Thank you
I got it

and i have try it

19

Seeding is related to Reproducibility of results.
Consider https://pytorch.org/docs/stable/notes/randomness.html
or any other newly-updated documentation to avoid (up-to-a-point) or ensure non-determinism.

20

Question about this - I have about 10 files all of which have import torch included. Do I need to call torch.manual_seed(0) on all of them? Or only on the first.

Thanks,
Jeremy

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