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randi

Uniformly distributed pseudorandom integers

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 indicate 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.

example

X = randi(___,typename) returns an array of pseudorandom integers between 1 and imax of data type typename. The typename input can be "single", "double", "int8", "uint8", "int16", "uint16", "int32", or "uint32". You can use any of the input arguments in the previous syntaxes.

example

X = randi(___,"like",p) returns an array of pseudorandom integers like p; that is, with the same data type and complexity (real or complex) as p. You can specify either typename or "like", but not both.

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.

X = randi(s,___) generates integers from random number stream s instead of the default global stream. To create a stream, use RandStream. You can specify s followed by any of the input argument combinations in previous syntaxes.

Examples

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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 = 5×5

     9     1     2     2     7
    10     3    10     5     1
     2     6    10    10     9
    10    10     5     8    10
     7    10     9    10     7

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 = 10×1

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

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 = 1×5

     9    10     2    10     7

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 = 1×5

     9    10     2    10     7

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

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

   408   457
   453   317
    64    49


X(:,:,2) =

   140   483
   274    79
   479   486


X(:,:,3) =

   479    71
   243   211
   401   458

Create a 1-by-4 vector of random numbers between 1 and 100 whose elements are of type int16.

r = randi(100,1,4,"int16")
r = 1x4 int16 row vector

   82   91   13   92

class(r)
ans = 
'int16'

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 = 2×2

     9     2
    10    10

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

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

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 = 2x2 int8 matrix

    9    2
   10   10

class(X)
ans = 
'int8'

Generate 10 random complex integers from the discrete uniform distribution over a square domain with real and imaginary parts in the interval [-5,5].

a = randi([-5,5],10,1,"like",1i)
a = 10×1 complex

   3.0000 + 4.0000i
  -4.0000 + 5.0000i
   1.0000 - 4.0000i
  -2.0000 + 1.0000i
   5.0000 + 5.0000i
  -4.0000 + 5.0000i
   5.0000 + 0.0000i
   3.0000 - 4.0000i
  -1.0000 + 5.0000i
   3.0000 + 5.0000i

Input Arguments

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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)

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.

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

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

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

Data type (class) to create, specified as "double", "single", "int8", "uint8", "int16", "uint16", "int32", "uint32", or the name of another class that provides randi support.

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

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

Random number stream, specified as a RandStream object.

Example: s = RandStream("dsfmt19937"); randi(s,[5,10],[3 1])

Tips

  • The sequence of numbers produced by randi is determined by the internal settings of the uniform pseudorandom number generator that underlies rand, randi, and randn. You can control that shared random number generator using rng.

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

Extended Capabilities

Version History

Introduced in R2008b

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Errors starting in R2013b