Thanks Kevin! A possibly dumb follow-up question: in your example,

entropy = 382193877439745928479635728

is it relevant that `entropy` is a long integer? I.e., what are the constraints on its value, can one use entropy = 1234 or entropy = 0 or entropy = 1 instead? On Mon, Jun 29, 2020 at 5:37 PM Kevin Sheppard <kevin.k.sheppard@gmail.com> wrote:

The best practice is to use a SeedSequence to spawn child SeedSequences, and then to use these children to initialize your generators or bit generators.

from numpy.random import SeedSequence, Generator, PCG64, default_rng

entropy = 382193877439745928479635728

seed_seq = SeedSequence(entropy)

NUM_STREAMS = 2**15

children = seed_seq.spawn(NUM_STREAMS)

# if you want the current best bit generator, which may change

rngs = [default_rng(child) for child in children]

# If you want the most control across version, set the bit generator

# this uses PCG64, which is the current default. Each bit generator needs to be wrapped in a generator

rngs = [Generator(PCG64(child)) for child in children]

Kevin

From: Evgeni Burovski Sent: Monday, June 29, 2020 2:21 PM To: Discussion of Numerical Python Subject: Re: [Numpy-discussion] reseed random generator (1.19)

(apologies for jumping into a conversation)

So what is the recommendation for instantiating a number of generators

with manually controlled seeds?

The use case is running a series of MC simulations with reproducible

streams. The runs are independent and are run in parallel in separate

OS processes, where I do not control the time each process starts

(jobs are submitted to the batch queue), so default seeding seems

dubious?

Previously, I would just do roughly

seeds = [1234, 1235, 1236, ...]

rngs = [np.random.RandomState(seed) for seed in seeds]

...

and each process operates with its own `rng`.

What would be the recommended way with the new `Generator` framework?

A human-friendly way would be preferable if possible.

Thanks,

Evgeni

On Mon, Jun 29, 2020 at 3:20 PM Kevin Sheppard

<kevin.k.sheppard@gmail.com> wrote:

If you want to use the same entropy-initialized generator for temporarily-reproducible experiments, then you can use

gen = np.random.default_rng()

state = gen.bit_generator.state

gen.standard_normal()

# 0.5644742559549797, will vary across runs

gen.bit_generator.state = state

gen.standard_normal()

# Always the same as before 0.5644742559549797

The equivalent to the old way of calling seed to reseed is:

SEED = 918273645

gen = np.random.default_rng(SEED)

gen.standard_normal()

# 0.12345677

gen = np.random.default_rng(SEED)

gen.standard_normal()

# Identical value

Rather than reseeding the same object, you just create a new object. At some point in the development of Generator both methods were timed and there was no performance to reusing the same object by reseeding.

Kevin

From: Neal Becker

Sent: Monday, June 29, 2020 1:01 PM

To: Discussion of Numerical Python

Subject: Re: [Numpy-discussion] reseed random generator (1.19)

I was using this to reset the generator, in order to repeat the same sequence again for testing purposes.

On Wed, Jun 24, 2020 at 6:40 PM Robert Kern <robert.kern@gmail.com> wrote:

On Wed, Jun 24, 2020 at 3:31 PM Neal Becker <ndbecker2@gmail.com> wrote:

Consider the following:

from numpy.random import default_rng

rs = default_rng()

Now how do I re-seed the generator?

I thought perhaps rs.bit_generator.seed(), but there is no such attribute.

In general, reseeding an existing generator instance is not a good practice. What effect are you trying to accomplish? I assume that you are asking this because you are currently using `RandomState.seed()`. In what circumstances?

The raw `bit_generator.state` property *can* be assigned to, in order to support some advanced use cases (mostly involving de/serialization and similar kinds of meta-programming tasks). It's also been helpful for me to construct worst-case scenarios for testing parallel streams. But it quite deliberately bypasses the notion of deriving the state from a human-friendly seed number.

--

Robert Kern

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