In earlier versions of MATLAB^{®}, you controlled the random
number generator used by the rand
and randn
functions with the 'seed'
, 'state'
or 'twister'
inputs.
For example:
rand('seed',sd) randn('seed',sd) rand('state',s) randn('state',s) rand('twister',5489)
These syntaxes referred to different types of generators, and they are no longer recommended for the following reasons:
The terms 'seed'
and 'state'
are
misleading names for the generators.
All of the generators except 'twister'
are
flawed.
They unnecessarily use different generators for rand
and randn
.
To assess the impact of replacing discouraged syntaxes in your existing code, execute the following commands at the start of your MATLAB session:
warning('on','MATLAB:RandStream:ActivatingLegacyGenerators') warning('on','MATLAB:RandStream:ReadingInactiveLegacyGeneratorState')
Use the rng
function to control the shared
generator used by rand
, randn
, randi
and
all other random number generation functions like randperm
, sprand
,
and so on. To learn how to use the rng
function
when replacing discouraged syntaxes, take a few moments to understand
their function. This should help you to see which new rng
syntax
best suits your needs.
The first input to rand(Generator,s)
or randn(Generator,s)
specified
the type of the generator, as described here.

The v4
and v5
generators
are no longer recommended unless you are trying to exactly reproduce
the random numbers generated in earlier versions of MATLAB. The
simplest way to update your code is to use rng
.
The rng
function replaces the names for the rand
and randn
generators
as follows.
rand/randn Generator Name  rng Generator Name 

'seed'  'v4' 
'state' 

'twister'  'twister' (recommended) 
The most common uses of the integer seed sd
in
the rand(Generator,sd)
syntax were to:
Reproduce exactly the same random numbers each time (e.g., by using a seed such as 0, 1, or 3141879)
Try to ensure that MATLAB always gives different
random numbers in separate runs (for example, by using a seed such
as sum(100*clock)
)
The following table shows replacements for syntaxes with an
integer seed sd
.
The first column shows the discouraged syntax with rand
and randn
.
The second column shows how to exactly reproduce the
discouraged behavior with the new rng
function.
In most cases, this is done by specifying a legacy generator type
such as the v4 or v5 generators, which is no longer recommended.
The third column shows the recommended alternative,
which does not specify the optional generator type input to rng
.
Therefore, if you always omit the Generator
input, rand
, randn
,
and randi
just use the default Mersenne Twister
generator that is used at MATLAB startup. In future releases
when new generators supersede the Mersenne Twister, this code will
use the new default.
Discouraged rand/randn Syntax  Not Recommended: Reproduce Discouraged Behavior Exactly By Specifying Generator Type  Recommended Alternative: Does Not Override Generator Type 

rand('twister',5489)  rng(5489,'twister')  rng('default') 
rand('seed',sd)  rng(sd,'v4')  rng(sd) 
randn('seed',sd)  
rand('state',sd)  rng(sd,'v5uniform')  
randn('state',sd)  rng(sd,'v5normal')  
rand('seed',sum(100*clock))  rng(sum(100*clock),'v4')  rng('shuffle') 
The most common use of the state vector (shown here as st
)
in the rand(Generator,st)
syntax was to reproduce
exactly the random numbers generated at a specific point in an algorithm
or iteration. For example, you could use this vector as an aid in
debugging.
The rng
function changes the pattern of
saving and restoring the state of the random number generator as shown
in the next table. The example in the left column assumes that you
are using the v5
uniform generator. The example
in the right column uses the new syntax, and works for any generator
you use.
Discouraged Syntax Using rand/randn  New Syntax Using rng 

% Save v5 generator state. st = rand('state'); % Call rand. x = rand; % Restore v5 generator state. rand('state',st); % Call rand again and hope % for the same results. y = rand  % Get generator settings. s = rng; % Call rand. x = rand; % Restore previous generator % settings. rng(s); % Call rand again and % get the same results. y = rand 
For a demonstration, see this instructional video.
If there is code that you are not able or not permitted to modify
and you know that it uses the discouraged random number generator
control syntaxes, it is important to remember that when you use that
code MATLAB will switch into legacy mode.
In legacy mode, rand
and randn
are
controlled by separate generators, each with their own settings.
Calls to rand
in legacy mode use one of
the following:
The 'v4'
generator, controlled
by rand('seed', ...)
The 'v5uniform'
generator, controlled
by rand('state', ...)
The 'twister'
generator, controlled
by rand('twister', ...)
Calls to randn
in legacy mode use one of
the following:
The 'v4'
generator, controlled
by randn('seed', ...)
The 'v5normal'
generator, controlled
by randn('state', ...)
If code that you rely on puts MATLAB into legacy mode, use the following command to escape legacy mode and get back to the default startup generator:
rng default
Alternatively, to guard around code that puts MATLAB into legacy mode, use:
s = rng % Save current settings of the generator. ... % Call code using legacy random number generator syntaxes. rng(s) % Restore previous settings of the generator.