Random Source
Generate randomly distributed values
 Library:
DSP System Toolbox / Sources
Description
The Random Source block generates a frame of M
values
drawn from a uniform or Gaussian pseudorandom distribution. Specify M
in the Samples per frame parameter.
Ports
Output
Port_1
— Signal of random values
scalar  vector  matrix
Signal of random values with uniform or Gaussian (normal) distribution.
Data Types: single
 double
Complex Number Support: Yes
Parameters
Source type
— Uniform or Gaussian
Uniform
(default)  Gaussian
The distribution from which to draw the random values,
Uniform
or
Gaussian
.
When you set the Source type parameter to
Uniform
, the output samples are drawn from a
uniform distribution whose minimum and maximum values are specified by the
Minimum and Maximum
parameters, respectively. All values in this range are equally likely to be
selected. A lengthN vector specified for one or both of
these parameters generates an Nchannel output
(MbyN matrix) containing a
unique random distribution in each channel.
For example, specify
Minimum =
[0 0 3 3]
Maximum =
[10 10 20 20]
to generate a fourchannel output whose first and second columns contain random values in the range [0, 10], and whose third and fourth columns contain random values in the range [3, 20]. When you specify only one of the Minimum and Maximum parameters as a vector, the block scalar expands the other parameter so it is the same length as the vector.
When you set the Source type parameter to
Gaussian
, you must also set the
Method parameter, which determines the method by
which the block computes the output.
Method
— Method of computing Gaussian random values
Ziggurat
(default)  Sum of uniform values
The method by which the block computes the Gaussian random values:
Ziggurat
— Produces Gaussian random values by using the ziggurat method.Sum of uniform values
— Produces Gaussian random values by adding and scaling uniformly distributed random signals based on the central limit theorem. This theorem states that the probability distribution of the sum of a sufficiently high number of random variables approaches the Gaussian distribution. You must set the Number of uniform values to sum parameter, which determines the number of uniformly distributed random numbers to sum to produce a single Gaussian random value.
For both settings of the Method parameter, the output samples are drawn from the normal distribution defined by the Mean and Variance parameters. A lengthN vector specified for one or both of the Mean and Variance parameters generates an Nchannel output (MbyN frame matrix) containing a distinct random distribution in each column. When you specify only one of these parameters as a vector, the block scalar expands the other parameter so it is the same length as the vector.
Dependencies
To enable this parameter, set Source type to
Gaussian
. For more information, see Source type.
Number of uniform values to sum
— Number of uniform values to sum
12
(default)
The number of uniformly distributed random values to sum to compute a single number in a Gaussian random distribution.
Dependencies
To enable this parameter, set Source type to
Gaussian
and Method
to Sum of uniform values
. For more
information, see Source type.
Minimum
— Minimum value of uniform distribution
0
(default)  scalar  vector
The minimum value in the uniform distribution specified as a finite scalar or vector.
Tunable: Yes
Dependencies
To enable this parameter, set Source type to
Uniform
.
Limitations
Tunable (Simulink) in Simulation mode only.
Maximum
— Maximum value of uniform distribution
1
(default)  scalar  vector
The maximum value in the uniform distribution specified as a finite scalar or vector.
Tunable: Yes
Dependencies
To enable this parameter, set Source type to
Uniform
.
Limitations
Tunable (Simulink) in Simulation mode only.
Mean
— Mean value of Gaussian distribution
0
(default)  scalar  vector
The mean of the Gaussian (normal) distribution specified as a finite scalar or vector.
Tunable: Yes
Dependencies
To enable this parameter, set Source type to
Gaussian
.
Limitations
Tunable (Simulink) in Simulation mode only.
Variance
— Variance of Gaussian distribution
1
(default)  scalar  vector
The variance of the Gaussian (normal) distribution.
Dependencies
To enable this parameter, set Source type to
Gaussian
.
Limitations
Tunable (Simulink) in Simulation mode only.
Repeatability
— Repeatability of block output
Specify seed
(default)  Repeatable
 Not repeatable
The Repeatability parameter determines if the block outputs the same signal each time you run the simulation. You can set the parameter to one of the following options:
Repeatable
— Outputs the same signal each time you run the simulation. The first time you run the simulation, the block randomly selects an initial seed. The block reuses these same initial seeds every time you rerun the simulation.Specify seed
— Outputs the same signal each time you run the simulation. Every time you run the simulation, the block uses the initial seeds specified in the Initial seed parameter. Also see Initial seed.Not repeatable
— Does not output the same signal each time you run the simulation. Every time you run the simulation, the block randomly selects an initial seed.
Initial seed
— Initial seed for random number generator
1
(default)  scalar  vector
The initial seed(s) to use for the random number generator specified as a finite scalar or vector. The generator produces an identical sequence of pseudorandom numbers each time it is executed with a particular initial seed.
To specify the N initial seeds for an
Nchannel realvalued output, set the
Complexity parameter to
Real
and provide one of the following in the
Initial seed parameter:
LengthN vector of initial seeds — Uses each vector element as an initial seed for the corresponding channel in the Nchannel output.
Single scalar — Uses the scalar to generate N random values as the seeds for the Nchannel output.
To specify the initial seeds for an Nchannel
complexvalued output, set the Complexity parameter to
Complex
and provide one of the following in
the Initial seed parameter:
LengthN vector of initial seeds — Uses each vector element as an initial seed for generating N channels of real random values. The block uses pairs of adjacent values in each of these channels as the real and imaginary components of the final output, as illustrated in the following figure.
Single scalar — Uses the scalar to generate N random values as the seeds for generating N channels of real random values. The block uses pairs of adjacent values in each of these channels as the real and imaginary components of the final output, as illustrated in the following figure.
Tunable: Yes
Dependencies
To enable this parameter, set Repeatability to
Specify seed
.
Limitations
Tunable (Simulink) in Simulation mode only.
Inherit output port attributes
— Inherit output port parameters from downstream block
off
(default)  on
When you select this check box, the block inherits the sample mode, sample time, output data type, complexity, and signal dimensions of the signal from the downstream block. When you select this check box, the Sample mode, Sample time, Samples per frame, Output data type, and Complexity parameters are disabled.
Suppose that you want to back propagate a 1D vector. The output of the
Random Source block is a 1D vector of length M, where
length M is inherited from the downstream block. When the
Minimum, Maximum,
Mean, or Variance parameter
specifies N channels, the 1D vector output contains
M/N samples from each channel. An
error occurs in this case when M is not an integer
multiple of N
.
Suppose that you want to back propagate a
MbyN signal. When
N>1
, your signal has
N channels. When N =
1
, your signal has M channels. The
value of the Minimum, Maximum,
Mean, or Variance parameter
can be a scalar or a vector of length equal to the number of channels. You
can specify these parameters as either row or column vectors, except when
the signal is a row vector. In this case, the Minimum,
Maximum, Mean, or
Variance parameter must also be specified as a row
vector.
Sample mode
— Discrete or continuous
Discrete
(default)  Continuous
The sample mode, specified as Continuous
or
Discrete
.
When you set Sample mode to
Discrete
, the Sample
time parameter value,
T_{s}, specifies the random
sequence sample period. In this mode, the block generates the number of
samples specified by the Samples per frame parameter
value, M, and outputs this frame with a period of
MT_{s}.
When you set Sample mode to
Continuous
, the block is configured for
continuoustime operation, and the Sample time and
Samples per frame parameters are disabled. Note
that many DSP System Toolbox™ blocks do not accept continuoustime inputs.
Dependencies
To enable this parameter, clear the Inherit output port attributes check box.
Sample time
— Output sample period
1
(default)  scalar
The sample period, T_{s}, of the
random output sequence when the Sample mode is
Discrete
, specified as a positive, finite,
scalar. The output frame period is
MT_{s}.
Dependencies
To enable this parameter, clear the Inherit output port
attributes check box and set Sample
mode to Discrete
.
Samples per frame
— Samples per output frame
1
(default)  positive integer
The number of samples, M, in each output frame, specified as a positive integer. The output frame period is MT_{s}.
Dependencies
To enable this parameter, clear the Inherit output port
attributes check box and set Sample
mode to Discrete
.
Output data type
— Output data type
Double
(default)  Single
The data type of the output, specified as singleprecision or doubleprecision.
Dependencies
To enable this parameter, clear the Inherit output port attributes check box.
Complexity
— Complexity of output
Real
(default)  Complex
The complexity of the output, specified as Real
or Complex
. These settings control all channels
of the output, so real and complex data cannot be combined in the same
output. For complex output with a Uniform
distribution, the real and imaginary components in each channel are both
drawn from the same uniform random distribution, defined by the
Minimum and Maximum parameters
for that channel.
For complex output with a Gaussian
distribution, the real and imaginary components in each channel are drawn
from normal distributions with different means. In this case, the
Mean parameter for each channel should specify a
complex value; the real component of the Mean parameter
specifies the mean of the real components in the channel, while the
imaginary component specifies the mean of the imaginary components in the
channel. When either the real or imaginary component is omitted from the
Mean parameter, a default value of 0 is used for
the mean of that component.
For example, a Mean parameter setting of
[5+2i 0.5 3i]
generates a threechannel output with
the following means.
Channel 1 mean  real = 5  imaginary = 2 
Channel 2 mean  real = 0.5  imaginary = 0 
Channel 3 mean  real = 0  imaginary = 3 
For complex output, the Variance parameter, σ^{2}, specifies the total variance for each output channel. This is the sum of the variances of the real and imaginary components in that channel.
$${\sigma}^{2}={\sigma}_{\mathrm{Re}}^{2}+{\sigma}_{\mathrm{Im}}^{2}$$
The specified variance is equally divided between the real and imaginary components, so that
$$\begin{array}{c}{\sigma}_{\mathrm{Re}}^{2}=\frac{{\sigma}^{2}}{2}\\ {\sigma}_{\mathrm{Im}}^{2}=\frac{{\sigma}^{2}}{2}\end{array}$$
Dependencies
To enable this parameter, clear the Inherit output port attributes check box.
Model Examples
Block Characteristics
Data Types 

Direct Feedthrough 

Multidimensional Signals 

VariableSize Signals 

ZeroCrossing Detection 

Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.
Generated code relies on the memcpy
or
memset
function (string.h
) under certain
conditions.
Version History
Introduced before R2006a
See Also
Blocks
 Discrete Impulse  Maximum  Minimum  Signal From Workspace  Standard Deviation  Variance  Constant (Simulink)  Random Number (Simulink)  Signal Generator (Simulink)
Functions
rand
randn
RandStream
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