Histogram
Histogram of input or sequence of inputs
Libraries:
DSP System Toolbox /
Statistics
Description
The Histogram block computes the frequency distribution of the input elements along each column or along the entire input. You can specify the dimension using the Find the histogram over parameter. The block distributes the input elements based on their value into a number of discrete bins specified by the Number of bins parameter. For more details, see Algorithms.
When the input data is real, the bin boundaries are cast into the double data type. When the input data is complex, bin boundaries for doubleprecision inputs are cast into double, and bin boundaries for integer inputs are cast into double and squared. For an example, see Compute the Histogram of Real and Complex Data.
To track the frequency distribution of inputs over a period of time, select the Running histogram parameter.
When the input is complex, the block sorts the elements by their magnitude.
Examples
Compute the Histogram of Real and Complex Data
Simulink^{®} model example that explains how the histogram bin boundaries are calculated based on the input.
Ports
Input
In — Data input
vector  matrix  ND array
The block accepts realvalued or complexvalued multichannel and multidimensional inputs. The input data type must be double precision, single precision, integer, or fixed point, with poweroftwo slope and zero bias.
This port is unnamed until you select the Running
histogram parameter and set the Reset
port parameter to any option other than
None
.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
 fixed point
 bus
Complex Number Support: Yes
Rst — Reset port
scalar
Specify the reset event that causes the block to reset the running histogram. The reset signal and the input data signal must have the same rate.
Dependencies
To enable this port, select the Running
histogram parameter, and set the Reset
port parameter to any option other than
None
.
Data Types: single
 double
 int8
 int16
 int32
 uint8
 uint16
 uint32
 Boolean
Output
Port_1 — Histogram output
vector  matrix  ND array
Outputs the histogram data as a vector, matrix, or array. The output primarily depends on the settings of the Running histogram and Find the histogram over parameters.
For example, consider a twodimensional input signal of size MbyN.
When you clear the Running histogram parameter, the block computes the frequency distribution in each column of input or along the entire input. When you set Find the histogram over to:
Each column
— The block computes a histogram for each column of the input. The output is an nbyN matrix, where n is the Number of bins. The jth column of the output matrix contains the histogram for the data in the jth column of the MbyN input matrix.Entire input
— The block computes a histogram for the entire input vector, matrix, or ND array. The output is an nby1 vector, where n is the Number of bins.
When you select the Running histogram parameter, the block computes the frequency distribution of all inputs over a period of time. In this case, when you set Find the histogram over to:
Each column
— The block computes a running histogram for each column of the input. The output is an nbyN matrix, where n is the Number of bins. The jth column of the output matrix contains the running histogram for the data in the jth column of the MbyN matrix input.Entire input
— The block computes the running histogram for the entire input vector, matrix, or ND array. The output is an nby1 vector, where n is the Number of bins.
The output data type is uint32
when the input has a
data type other than single
or
double
. The largest number that can be
represented by uint32
is
2^{32}1
. If the
range of any input exceeds this value, the block wraps the value back to
0
.
Data Types: single
 double
 uint32
Parameters
Main Tab
Lower limit of histogram — Lower boundary of lowestvalued bin
scalar
Specify the lower boundary of the lowestvalued bin as a real scalar.
This parameter does not accept NaN
or
Inf
. If the input has a value less than
Lower limit of histogram, the block places this
element in the lowestvalued bin.
Upper limit of histogram — Upper boundary of highestvalued bin
scalar
Specify the upper boundary of the highestvalued bin as a real scalar.
This parameter does not accept NaN
or
Inf
. If the input has a value greater than
Upper limit of histogram, the block places this
element in the highestvalued bin.
Number of bins — Number of histogram bins
positive integer
Specify the number of histogram bins as a positive integer.
Find the histogram over — Compute histogram over each column or entire input
Each column
(default)  Entire input
Specify whether the histogram is computed over each column or the entire input. The options for this parameter are affected by the setting of the Running histogram parameter.
When you clear the Running histogram parameter, and you set Find the histogram over parameter to:
Each column
— The block computes the histogram over each column.Entire input
— The block outputs the histogram over the entire input.
When you select the Running histogram parameter, and you set Find the histogram over parameter to:
Each column
— The block computes the running histogram over each column.Entire input
— The block outputs the running histogram over the entire input.
Normalized — Normalize output
off (default)  on
When you select this parameter, the block output,
y, is normalized. In mathematical terms,
sum(y) = 1
. This parameter
does not apply for fixedpoint input signals.
Running histogram — Track frequency distribution over time
off (default)  on
When you select this parameter, the block tracks the frequency distribution of inputs over a period of time.
Reset port — Reset event
Nonzero sample
(default)  None
 Rising edge
 Falling edge
 Either edge
The block resets the running histogram and empties all the bins whenever a reset event is detected at the optional Rst port. The reset sample time must equal the input sample time.
Use this parameter to specify the reset event:
Nonzero sample
— Triggers a reset operation at each sample time when the Rst input is not zero.None
— Disables the Rst port.Rising edge
— Triggers a reset operation when the Rst input does one of the following:Rises from a negative value to either a positive value or zero.
Rises from zero to a positive value, where the rise is not a continuation of a rise from a negative value to zero.
Falling edge
— Triggers a reset operation when the Rst input does one of the following:Falls from a positive value to a negative value or zero.
Falls from zero to a negative value, where the fall is not a continuation of a fall from a positive value to zero.
Either edge
— Triggers a reset operation when the Rst input is aRising edge
orFalling edge
.
Note
When running simulations in the Simulink multitasking mode, reset signals have a onesample latency. When the block detects a reset event, there is a onesample delay at the reset port rate before the block applies the reset. For more information on latency and the Simulink tasking modes, see Excess Algorithmic Delay (Tasking Latency) and TimeBased Scheduling and Code Generation (Simulink Coder).
Dependencies
To enable this parameter, select the Running histogram parameter.
Data Types Tab
Note
To use these parameters, the data input must be complex and fixed point. For all other inputs, the parameters on the Data Types tab are ignored.
Rounding mode — Method of rounding operation
Floor
(default)  Ceiling
 Convergent
 Nearest
 Round
 Simplest
 Zero
Specify the rounding mode for fixedpoint operations. For more details, see rounding mode.
Saturate on integer overflow — Method of overflow action
off (default)  on
When you select this parameter, the block saturates the result of its
fixedpoint operation. When you clear this parameter, the block wraps
the result of its fixedpoint operation. For details on
saturate
and wrap
, see overflow
mode for fixedpoint operations.
Product output — Product output data type
Inherit: Same as
input
(default)  fixdt([],16,0)
The squares of the real and imaginary parts of the complex input are stored in the Product output data type.
You can set this parameter to:
Inherit: Same as input
— The product output data type is the same as the input data type.fixdt([],16,0)
— The product output data type is an autosigned, binarypoint, scaled, fixedpoint data type with a word length of 16 bits and a fraction length of 0.
Alternatively, you can set the Product output data type by using the Data Type Assistant. To use the assistant, click the Show data type assistant button.
For more information on the data type assistant, see Specify Data Types Using Data Type Assistant (Simulink).
Accumulator — Accumulator data type
Inherit: Same as
input
(default)  Inherit: Same as product output
 fixdt([],16,0)
The result of the sum of the squares of the real and imaginary parts of the complex input are stored in the Accumulator data type.
You can set this parameter to:
Inherit: Same as input
— The accumulator data type is the same as the input data type.Inherit: Same as product output
— The accumulator data type is the same as the product output data type.fixdt([],16,0)
— The accumulator data type is an autosigned, binarypoint, scaled, fixedpoint data type with a word length of 16 bits and a fraction length of 0.
Alternatively, you can set the Accumulator data type by using the Data Type Assistant. To use the assistant, click the Show data type assistant button.
For more information on the data type assistant, see Specify Data Types Using Data Type Assistant (Simulink).
Lock data type settings against changes by the fixedpoint tools — Prevent fixedpoint tools from overriding data types
off (default)  on
Select this parameter to prevent the fixedpoint tools from overriding the data types you specify on the block.
Block Characteristics
Data Types 

Direct Feedthrough 

Multidimensional Signals 

VariableSize Signals 

ZeroCrossing Detection 

More About
FixedPoint Data Types
The parameters on the Data Types tab are used only for complex fixedpoint inputs. Complex inputs are sorted by magnitude, which is the sum of the squares of the real and imaginary components of the input. The results of the squares of the real and imaginary parts are stored in the Product output data type. The result of the sum of the squares is stored in the Accumulator data type. The parameters on the Data Types tab are ignored for all other inputs.
Algorithms
Histogram
The histogram value for a given bin represents the frequency of occurrence of the input values bracketed by that bin. Upper limit of histogram specifies the upper boundary of the highestvalued bin, B_{M}. Lower limit of histogram specifies the lower boundary of the lowestvalued bin, B_{m}. The bins have equal width, given by:
$$\Delta =\frac{{B}_{M}{B}_{m}}{n}.$$
The bins are centered at the following locations:
$${B}_{m}+\left(k+\frac{1}{2}\right)\Delta \begin{array}{cccc}& & & k=0,1,2,\mathrm{...},n1\end{array}.$$
n is the number of bins, specified by the Number of bins parameter.
Input values that fall on the border between two bins are placed into the lowervalued bin. Each bin includes its upper boundary. For example, a bin of width 4 centered on the value 5 contains the input value 7, but not 3. Input values greater than the Upper limit of histogram parameter are placed in the highestvalued bin. Similarly, values less than the Lower limit of histogram parameter are placed in the lowestvalued bin.
The block sorts the complex data into bins by magnitude. The magnitude is the sum of the squares of the real and imaginary components of the complex data.
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
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