randi

Uniformly distributed pseudorandom integers

Syntax

  • X = randi(imax,classname)
  • X = randi(imax,n,classname)
  • X = randi(imax,sz1,...,szN,classname) example
  • X = randi(imax,sz,classname)
  • X = randi(imax,'like',p)
  • X = randi(imax,n,'like',p)
  • X = randi(imax,sz1,...,szN,'like',p)
  • X = randi(imax,sz,'like',p) example
  • X = randi([imin,imax],___)

Description

X = randi(imax) returns a pseudorandom scalar integer between 1 and imax.

example

X = randi(imax,n) returns an n-by-n matrix of pseudorandom integers drawn from the discrete uniform distribution on the interval [1,imax].

example

X = randi(imax,sz1,...,szN) returns an sz1-by-...-by-szN array where sz1,...,szN indicates the size of each dimension. For example, randi(10,3,4) returns a 3-by-4 array of pseudorandom integers between 1 and 10.

example

X = randi(imax,sz) returns an array where size vector sz defines size(X). For example, randi(10,[3,4]) returns a 3-by-4 array of pseudorandom integers between 1 and 10.

X = randi(imax,classname) returns a pseudorandom integer where classname specifies the data type. classname can be 'single', 'double', 'int8', 'uint8', 'int16', 'uint16', 'int32', or 'uint32'.

X = randi(imax,n,classname) returns an n-by-n array of data type classname.

example

X = randi(imax,sz1,...,szN,classname) returns an sz1-by-...-by-szN array of data type classname..

X = randi(imax,sz,classname) returns an array where size vector sz defines size(X) and classname defines class(X).

X = randi(imax,'like',p) returns a pseudorandom integer like p; that is, with the same data type (class).

X = randi(imax,n,'like',p) returns an n-by-n array like p.

X = randi(imax,sz1,...,szN,'like',p) returns an sz1-by-...-by-szN array like p.

example

X = randi(imax,sz,'like',p) returns an array like p where size vector sz defines size(X).

X = randi([imin,imax],___) returns an array containing integers drawn from the discrete uniform distribution on the interval [imin,imax], using any of the above syntaxes.

The sequence of numbers produced by randi is determined by the settings of the uniform random number generator that underlies rand, randn, and randi. The randi function uses one uniform random value to create each integer random value. You can control that shared random number generator using rng.

Examples

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Square Matrix of Random Integers

Generate a 5-by-5 matrix of random integers between 1 and 10. The first input to randi indicates the largest integer in the sampling interval (the smallest integer in the interval is 1).

r = randi(10,5)
r =

     4     3     2    10     5
     6     5     4    10     6
     5     1     2     1    10
     7    10     5     8     5
     7     2     4     3    10

Random Integers Within Specified Interval

Generate a 10-by-1 column vector of uniformly distributed random integers from the sample interval [-5,5].

r = randi([-5,5],10,1)
r =

     3
     4
    -4
     5
     1
    -4
    -2
     1
     5
     5

Control Random Number Generation

Save the current state of the random number generator and create a 1-by-5 vector of random integers.

s = rng;
r = randi(10,1,5)
r =

     1     6     9     7     2

Restore the state of the random number generator to s, and then create a new 1-by-5 vector of random integers. The values are the same as before.

rng(s);
r1 = randi(10,1,5)
r1 =

     1     6     9     7     2

Always use the rng function (rather than the rand or randn functions) to specify the settings of the random number generator. For more information, see Replace Discouraged Syntaxes of rand and randn.

3-D Array of Random Integers

Create a 3-by-2-by-3 array of uniformly distributed random integers between 1 and 500.

X = randi(500,[3,2,3])
X(:,:,1) =

   185    79
   231   428
   491   323


X(:,:,2) =

   189   242
    96    61
   215   295


X(:,:,3) =

   114   126
   193   146
   292   309

Random Integers of Other Data Types

Create a 1-by-4 vector of random numbers whose elements are of type int16.

r = randi(100,1,4,'int16')
r =

     28     55     96     97
class(r)
ans =

int16

Size Defined by Existing Array

Create a matrix of uniformly distributed random integers between 1 and 10 with the same size as an existing array.

A = [3 2; -2 1];
sz = size(A);
X = randi(10,sz)
X =

     3    10
     9     8

It is a common pattern to combine the previous two lines of code into a single line:

X = randi(10,size(A));

Size and Numeric Data Type Defined by Existing Array

Create a 2-by-2 matrix of 8-bit signed integers.

p = int8([3 2; -2 1]);

Create an array of random integers that is the same size and data type as p.

X = randi(10,size(p),'like',p)
X =

    4    2
    6   10
class(X)
ans =

int8

Input Arguments

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imax — Largest integer in sample intervalpositive integer

Largest integer in sample interval, specified as a positive integer. randi draws values from the uniform distribution in the sample interval [1,imax].

Example: randi(10,5)

imin — Smallest integer in sample interval1 (default) | scalar integer

Smallest integer in sample interval, specified as a scalar integer.

Both imin and imax must be integers that satisfy iminimax.

For example, randi([50,100],5) returns a 5-by-5 matrix of random integers between (and including) 50 and 100.

n — Size of square matrixinteger value

Size of square matrix, specified as an integer value.

  • If n is 0, then X is an empty matrix.

  • If n is negative, then it is treated as 0.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

sz1,...,szN — Size of each dimension (as separate arguments)two or more integer values

Size of each dimension, specified as separate arguments of integer values.

  • If the size of any dimension is 0, then X is an empty array.

  • If the size of any dimension is negative, then it is treated as 0.

  • Beyond the second dimension, randi ignores trailing dimensions with a size of 1. For example, randi([5,10],3,1,1,1) produces a 3-by-1 vector of random integers between 5 and 10.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

sz — Size of each dimension (as a row vector)integer values

Size of each dimension, specified as a row vector of integer values. Each element of this vector indicates the size of the corresponding dimension:

  • If the size of any dimension is 0, then X is an empty array.

  • If the size of any dimension is negative, then it is treated as 0.

  • Beyond the second dimension, randi ignores trailing dimensions with a size of 1. For example, randi([5,10],[3,1,1,1]) produces a 3-by-1 vector of random integers between 5 and 10.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

classname — Data type (class) to create'double' (default) | 'single' | 'int8' | 'uint8' | ...

Output class, specified as the string 'double', 'single', 'int8', 'uint8', 'int16', 'uint16', 'int32', 'uint32', or the name of another class that provides randi support.

Example: randi(5,5,'int8')

Data Types: char

p — Prototype of array to createnumeric array

Prototype of array to create, specified as a numeric array.

Example: randi(5,5,'like',p)

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32
Complex Number Support: Yes

More About

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Tips

  • The arrays returned by randi might contain repeated integer values. This behavior is sometimes referred to as sampling with replacement. Use randperm if you require all unique values.

See Also

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