## Create Arrays of Random Numbers

MATLAB® uses algorithms to generate pseudorandom and pseudoindependent numbers. These numbers are not strictly random and independent in the mathematical sense, but they pass various statistical tests of randomness and independence, and their calculation can be repeated for testing or diagnostic purposes.

The `rand`, `randi`, `randn`, and `randperm` functions are the primary functions for creating arrays of random numbers. The `rng` function allows you to control the seed and algorithm that generates random numbers.

### Random Number Functions

There are four fundamental random number functions: `rand`, `randi`, `randn`, and `randperm`. The `rand` function returns floating-point numbers between 0 and 1 that are drawn from a uniform distribution. For example, create a 1000-by-1 column vector containing real floating-point numbers drawn from a uniform distribution.

```rng("default") r1 = rand(1000,1);```
All the values in `r1` are in the open interval (0,1). A histogram of these values is roughly flat, which indicates a fairly uniform sampling of numbers.

The `randi` function returns `double` integer values drawn from a discrete uniform distribution. For example, create a 1000-by-1 column vector containing integer values drawn from a discrete uniform distribution.

`r2 = randi(10,1000,1);`
All the values in `r2` are in the close interval [1, 10]. A histogram of these values is roughly flat, which indicates a fairly uniform sampling of integers between 1 and 10.

The `randn` function returns arrays of real floating-point numbers that are drawn from a standard normal distribution. For example, create a 1000-by-1 column vector containing numbers drawn from a standard normal distribution.

`r3 = randn(1000,1);`
A histogram of `r3` looks like a roughly normal distribution whose mean is 0 and standard deviation is 1.

You can use the `randperm` function to create a `double` array of random integer values that have no repeated values. For example, create a 1-by-5 array containing integers randomly selected from the range [1, 15].

`r4 = randperm(15,5);`
Unlike `randi`, which can return an array containing repeated values, the array returned by `randperm` has no repeated values.

Successive calls to any of these functions return different results. This behavior is useful for creating several different arrays of random values.

### Random Number Generators

MATLAB offers several generator algorithm options, which are summarized in the table.

ValueGenerator NameGenerator Keyword
`"twister"`Mersenne Twistermt19937ar
`"simdTwister"`SIMD-Oriented Fast Mersenne Twisterdsfmt19937
`"combRecursive"`Combined Multiple Recursivemrg32k3a
`"multFibonacci"`Multiplicative Lagged Fibonaccimlfg6331_64
`"philox"`Philox 4x32 generator with 10 roundsphilox4x32_10
`"threefry"`Threefry 4x64 generator with 20 roundsthreefry4x64_20
`"v4"`Legacy MATLAB version 4.0 generatormcg16807
`"v5uniform"`Legacy MATLAB version 5.0 uniform generatorswb2712
`"v5normal"`Legacy MATLAB version 5.0 normal generatorshr3cong

Use the `rng` function to set the seed and generator used by the `rand`, `randi`, `randn`, and `randperm` functions.

For example, `rng(0,"twister")` sets the seed to 0 and the generator algorithm to Mersenne Twister. To avoid repetition of random number arrays when MATLAB restarts, see Why Do Random Numbers Repeat After Startup?

For more information about controlling the random number generator's state to repeat calculations using the same random numbers, or to guarantee that different random numbers are used in repeated calculations, see Controlling Random Number Generation.

You can set the default algorithm and seed in MATLAB preferences (since R2023b). If you do not change these preferences, then `rng` uses the factory value of `"twister"` for the Mersenne Twister generator with seed 0, as in previous releases. For more information, see Default Settings for Random Number Generator and Reproducibility for Random Number Generator.

### Random Number Data Types

`rand` and `randn` functions generate values in double precision by default.

```rng("default") A = rand(1,5); class(A)```
`ans = 'double'`

To specify the class as double explicitly:

```rng("default") B = rand(1,5,"double"); class(B)```
`ans = 'double'`
`isequal(A,B)`
```ans = 1```

`rand` and `randn` can also generate values in single precision.

```rng("default") A = rand(1,5,"single"); class(A)```
`ans = 'single'`

The values are the same as if you had cast the double precision values from the previous example. The random stream that the functions draw from advances the same way regardless of what class of values is returned.

`A,B`
```A = 0.8147 0.9058 0.1270 0.9134 0.6324 B = 0.8147 0.9058 0.1270 0.9134 0.6324```

`randi` supports both integer types and single or double precision.

```A = randi([1 10],1,5,"double"); class(A)```
```ans = 'double' ```
```B = randi([1 10],1,5,"uint8"); class(B)```
```ans = 'uint8' ```