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Random Number

Generate normally distributed random numbers

Library

Sources

Description

The Random Number block generates normally distributed random numbers. To generate uniformly distributed random numbers, use the Uniform Random Number block.

You can generate a repeatable sequence using any Random Number block with the same nonnegative seed and parameters. The seed resets to the specified value each time a simulation starts. By default, the block produces a sequence that has a mean of 0 and a variance of 1. To generate a vector of random numbers with the same mean and variance, specify the Seed parameter as a vector.

Avoid integrating a random signal, because solvers must integrate relatively smooth signals. Instead, use the Band-Limited White Noise block.

The numeric parameters of this block must have the same dimensions after scalar expansion. If you select the Interpret vector parameters as 1-D check box and the numeric parameters are row or column vectors after scalar expansion, the block outputs a 1-D signal. If you clear the Interpret vector parameters as 1-D check box, the block outputs a signal of the same dimensionality as the parameters.

Data Type Support

The Random Number block outputs a real signal of type double. For more information, see Data Types Supported by Simulink in the Simulink® documentation.

Parameters and Dialog Box

Mean

Specify the mean of the random numbers. The default is 0.

Variance

Specify the variance of the random numbers. The default is 1.

Seed

Specify the starting seed for the random number generator. The default is 0.

The seed must be 0 or a positive integer. Output is repeatable for a given seed.

Sample time

Specify the time interval between samples. The default is 0.1, which matches the default sample time of the Band-Limited White Noise block. See Specify Sample Time in the Simulink documentation for more information.

Interpret vector parameters as 1-D

If you select this check box and the other parameters are row or column vectors after scalar expansion, the block outputs a 1-D signal. Otherwise, the block outputs a signal of the same dimensionality as the other parameters. For more information, see Determining the Output Dimensions of Source Blocks in the Simulink documentation.

Characteristics

Sample Time

Specified in the Sample time parameter

Scalar Expansion

Yes, of parameters

Dimensionalized

Yes

Multidimensionalized

Yes

Zero-Crossing Detection

No

Algorithm

mcg16807, multiplicative congruential generator

The generator algorithm is identical to the one used in MATLAB Version 4.0 by the rand and randn functions. For details on the mcg16807 algorithm, see Choosing a Random Number Generator in the MATLAB® documentation.

To use other algorithms supported by MATLAB in a Simulink model, generate a stream of random numbers in MATLAB, and store the output as a .mat file. Use this .mat file as the random number input for your simulation. For more information, see Creating and Controlling a Random Number Stream. To create multiple independent streams using MATLAB, see Multiple streams.

    Note:   Using multiple seeds to generate multiple parallel independent streams for a generator algorithm is not recommended for the mcg16807 algorithm. Instead, use the method described above.

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