rng - Control random number generator

rng - Control random number generator - MATLAB

Control random number generator

Syntax

Description

rng(seed) specifies the seed for the random number generator using the current generator algorithm.

Specify seed as a nonnegative integer, such as rng(1), to initialize the random number generator with that seed.
Specify seed as "shuffle" to initialize the generator seed based on the current time.

rng(seed,generator) also specifies the algorithm for the random number generator to use. For example, rng(2,"philox") initializes the Philox 4x32 generator with a seed of 2.

example

rng(generator) specifies the algorithm for the random number generator to use with a seed of 0. This syntax is equivalent to rng(0,generator). (since R2023b)

rng(s) initializes the generator based on the settings contained in a structure s with fields Type, Seed, and State. The structure s must be a structure that is returned by a previous call to s = rng or s = rng(__).

example

t = rng returns the current random number generator settings in a structure t with fields Type, Seed, and State.

example

t = rng(___) returns the current random number generator settings in a structure t before changing the settings using the specified arguments. You can specify the output argument with any of the input argument combinations in the previous syntaxes.

Examples

collapse all

Initialize the random number generator using the default generator algorithm and seed.

Show the default random number generator settings. In this case, the random number generator is using the Mersenne Twister algorithm with seed 0.

s = struct with fields:
     Type: 'twister'
     Seed: 0
    State: [625×1 uint32]

Create a 4-by-4 matrix of uniformly distributed random numbers between 0 and 1.

r = 4×4

    0.8147    0.6324    0.9575    0.9572
    0.9058    0.0975    0.9649    0.4854
    0.1270    0.2785    0.1576    0.8003
    0.9134    0.5469    0.9706    0.1419

Starting in R2023b, you can set the default algorithm and seed from the MATLAB Settings Window window. If you do not change the MATLAB settings, then rng uses the factory value of "twister" for the Mersenne Twister generator with seed 0, as in previous releases.

Specify the random number generator settings to make the results in this example repeatable. Set the generator seed to 2 and the algorithm to Mersenne Twister, and then save the generator settings.

s = struct with fields:
     Type: 'twister'
     Seed: 2
    State: [625×1 uint32]

Create a 1-by-5 row vector of random values between 0 and 1.

x = 1×5

    0.4360    0.0259    0.5497    0.4353    0.4204

Change the generator seed and algorithm, and create a new random row vector.

rng(1,"philox")
xnew = rand(1,5)

xnew = 1×5

    0.5361    0.2319    0.7753    0.2390    0.0036

Now restore the original generator settings and create a random vector. The result matches the original row vector x created with the original generator.

xold = 1×5

    0.4360    0.0259    0.5497    0.4353    0.4204

Input Arguments

collapse all

Random number seed, specified as a nonnegative integer less than 2^32 or "shuffle". When you specify seed as "shuffle", the rng function initializes the generator seed based on the current time, resulting in a different sequence of random numbers after each call to rng.

Random number algorithm, specified as one of the options in the table. For more information on generator algorithms, see Creating and Controlling a Random Number Stream.

Value	Generator Name	Generator Keyword
`"twister"`	Mersenne Twister	mt19937ar
`"simdTwister"`	SIMD-Oriented Fast Mersenne Twister	dsfmt19937
`"combRecursive"`	Combined Multiple Recursive	mrg32k3a
`"multFibonacci"`	Multiplicative Lagged Fibonacci	mlfg6331_64
`"philox"`	Philox 4x32 generator with 10 rounds	philox4x32_10
`"threefry"`	Threefry 4x64 generator with 20 rounds	threefry4x64_20

For legacy generators used in MATLAB versions 4.0 and 5.0, use one of these options.

Value	Generator Name	Generator Keyword
`"v4"`	Legacy MATLAB version 4.0 generator	mcg16807
`"v5uniform"`	Legacy MATLAB version 5.0 uniform generator	swb2712
`"v5normal"`	Legacy MATLAB version 5.0 normal generator	shr3cong

Random number generator settings, specified as a structure with fields Type, Seed, and State.

More About

collapse all

You can change the default algorithm and seed for the random number generator from the MATLAB Settings window. On the Home tab, in the Environment section, click Settings. Select > , and then select a different option for Default algorithm and select a different value for Default seed in the Random Number Generation setting. (since R2023b)
When you first start a MATLAB session or call rng("default"), MATLAB initializes the random number generator using the default algorithm and seed that you have set in the MATLAB settings. If you do not change the Random Number Generation setting, then rng uses the factory value of "twister" for the Mersenne Twister generator with seed 0, as in previous releases.
If you use parallel workers (requires Parallel Computing Toolbox™), rng("default") initializes the Threefry 4x64 generator with 20 rounds and a seed value of 0. Changing the default generator settings in the MATLAB Settings window does not affect the default behavior of the parallel workers. (since R2023a)

Use rng("default") at the start of your program if you want results to be repeatable within a MATLAB session. rng("default") uses the default algorithm and seed that are specified in your MATLAB settings. However, this command does not guarantee the same results between different MATLAB sessions with different settings.

Instead, use rng(seed,generator) or rng(generator) at the start of your program if you want results to remain the same in future MATLAB releases or when the default algorithm and seed have been changed in your MATLAB settings. For example, use rng("twister") to use the Mersenne Twister generator with seed 0.

The rng function is a pseudorandom number generator, which creates a deterministic sequence of numbers that appear random. These numbers are predictable if the seed and the deterministic algorithm of the generator are known. While not truly random, the generated numbers pass various statistical tests of randomness, satisfying the independent and identically distributed (i.i.d.) condition, and justifying the name pseudorandom.

Tips

When you perform parallel processing, do not use rng("shuffle") to set the random number stream on different workers for independent streams because it seeds the random number generator based on the current time. The rng function uses the same seed when the command is sent to multiple workers simultaneously, such as inside a parfor job. For independent streams on the workers, use the default behavior or consider using a unique substream on each worker using RandStream.
When you perform parallel processing, the default random number generators on the MATLAB client and MATLAB workers are different. By default, the MATLAB client uses the Mersenne Twister generator with seed 0 and the MATLAB workers use the Threefry 4x64 generator with 20 rounds with seed 0. Changing the default generator settings in the MATLAB Settings affects only the default behavior of the client and does not affect the default behavior of the parallel workers. If you need to generate the same random stream of numbers on the client and workers, you can use rng with the same generator algorithm and seed (or consider using RandStream with the same generator algorithm, seed, and normal transformation algorithm). For more information, see Control Random Number Streams on Workers (Parallel Computing Toolbox).
To use rng instead of the rand or randn functions with the "seed", "state", or "twister" inputs, see Replace Discouraged Syntaxes of rand and randn.

Extended Capabilities

expand all

Usage notes and limitations:

Only the "twister", "v5normal", and "v4" generators are supported.
The generated code for rng("shuffle") might produce different seeds than MATLAB produces.
For a MEX target:
- If extrinsic calls are disabled or rng is called inside a parfor-loop, the output of rng in the MEX function is not compatible with the rng function in MATLAB. You cannot pass the output of s = rng from the MEX function to rng in MATLAB.
- If extrinsic calls are enabled and rng is not called from inside a parfor-loop, only rng can access the data in the structure that rng returns.
- If extrinsic calls are enabled and rng is not called from inside a parfor-loop, generated MEX files use the same random number state as MATLAB in serial code. Otherwise, the generated MEX code and standalone code maintain their own random number state that is initialized to the same state as MATLAB.

Version History

Introduced in R2011a

expand all

Use the new syntax rng(generator) to specify the algorithm for the random number generator to use. This syntax allows you to set the random number algorithm without specifying the seed, where rng uses a seed of 0. This syntax is equivalent to rng(0,generator). For example, rng("philox") initializes the Philox 4x32 generator with a seed of 0.

You can change the default algorithm and seed for the random number generator from the MATLAB Settings Window window. On the Home tab, in the Environment section, click Settings. Select > , and then select a different option for Default algorithm and select a different value for Default seed in the Random Number Generation setting.

When you first start a MATLAB session or call rng("default"), MATLAB initializes the random number generator using the default algorithm and seed that you have set in the MATLAB settings. If you do not change the Random Number Generation setting, then rng uses the factory value of "twister" for the Mersenne Twister generator with seed 0, as in previous releases.

To access and modify settings for the random number generator programmatically, you can access the matlab.general.randomnumbers settings using the root SettingsGroup object returned by the settings function. For example, show the default algorithm and seed that you have set for the random number generator.

s = settings;
s.matlab.general.randomnumbers.DefaultAlgorithm
s.matlab.general.randomnumbers.DefaultSeed

When you perform parallel processing (requires Parallel Computing Toolbox), by default, the MATLAB client uses the Mersenne Twister random number generator with seed 0 and the MATLAB workers use the Threefry 4x64 generator with 20 rounds with seed 0. Changing the default generator settings in the MATLAB Settings window or using the matlab.general.randomnumbers settings affects only the default behavior of the client and does not affect the default behavior of the parallel workers.

When you use the syntax rng("default") on MATLAB parallel workers (requires Parallel Computing Toolbox), MATLAB resets the random number generator settings to the worker default values. The default corresponds to the Threefry 4x64 generator with 20 rounds and a seed value of 0.

In previous releases, when you use rng("default") on parallel workers, MATLAB changes the worker random number generator settings to the client default values. The default corresponds to the Mersenne Twister generator with a seed value of 0.

Syntax

Description

Examples

Input Arguments

More About

Tips

Extended Capabilities

Version History

See Also

Functions

Objects

Topics