Replace Discouraged Syntaxes of rand and randn
Description of the Discouraged Syntaxes
In earlier versions of MATLAB®, you controlled the random number generator used by the
randn functions with the
'twister' inputs. For
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:
'state'are misleading names for the generators.
All of the generators except
They unnecessarily use different generators for
To assess the impact of replacing discouraged syntaxes in your existing code, execute the following commands at the start of your MATLAB session:
Description of Replacement Syntaxes
rng function to control the shared generator used by
randi and all other random number generation functions like
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
randn(Generator,s) specified the type of the generator, as
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
function replaces the names for the
randn generators as follows.
|rand/randn Generator Name||rng Generator Name|
Replacement Syntaxes for Initializing the Generator with an Integer Seed
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
The following table shows replacements for syntaxes with an integer seed
The first column shows the discouraged syntax with
The second column shows how to exactly reproduce the discouraged behavior with the new
rngfunction. 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
randijust 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|
Replacement Syntaxes for Initializing the Generator with a State Vector
The most common use of the state vector (shown here as
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.
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
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 You Are Unable to Upgrade from Discouraged Syntax
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,
randn are controlled by
separate generators, each with their own settings.
rand in legacy mode use one of the following:
'v4'generator, controlled by
'v5uniform'generator, controlled by
'twister'generator, controlled by
randn in legacy mode use one of the
'v4'generator, controlled by
'v5normal'generator, controlled by
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:
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.