While Iterator
Control block for while-iterator subsystem
Description
The While Iterator block, when placed in a Subsystem
block, repeatedly executes the contents of the subsystem during the current time step
while the value of the input condition is true or 1
. Use this block
to implement the block diagram equivalent of a while
loop in a
programming language.
The While Iterator Subsystem block is preconfigured with a While Iterator block. Placing a While Iterator block in a Subsystem block makes it an atomic subsystem.
Examples
Simulink Subsystem Semantics
This set of examples shows different types of Simulink® Subsystems and what semantics are used when simulating these subsystems. Each example provides a description of the model and the subtleties governing how the model is executed.
Parallel Channel Power Allocation
A potential use of the Find Nonzero Elements block. This block outputs a variable-size signal containing the indices of the nonzero values of the input.
Ports
Input
cond — Logical condition signal
scalar
Signal with the result from evaluating a logical condition. Because
the subsystem is not externally triggered during a time step, evaluating
a condition as true (1
) or false
(0
) must reside within the subsystem.
The data type and values of the signal can be:
Logical (Boolean) — true (
1
) or false (0
).Numerical — true (any positive or negative number) or false (
0
).
Data Types: single
| double
| int8
| int16
| int32
| uint8
| uint16
| uint32
| Boolean
| fixed point
IC — Initial logical condition
scalar
Signal with the initial logical condition. At the beginning of each time step:
If
IC
is false (0
), the subsystem does not execute during the time step.If
IC
is true (value not equal to0
), the subsystem starts executing and continues to repeat execution as long as thecond
signal is true.
Data Types: single
| double
| int8
| int16
| int32
| uint8
| uint16
| uint32
| Boolean
| fixed point
Output Arguments
Iteration number — Signal with the number of iterations
scalar
Signal with the number of While Iterator Subsystem block executions during each time step.
Data Types: double
| int8
| int16
| int32
Parameters
Maximum number of iterations — Specify maximum number of iterations
-1
(default) | integer
Specify maximum number of iterations allowed during a time step.
-1
Any number of iterations as long as the
cond
signal is true (value not equal to0
). If you specify-1
and thecond
signal never becomes false (0
), the simulation runs in an infinite loop. In this case, the only way to stop the simulation is to terminate MATLAB®.- integer
Maximum number of iterations during a time step.
Programmatic Use
Block Parameter:
MaxIters |
Type: character vector |
Values: '5'
| '-1' | integer in quotes |
Default:
'5' |
While loop type — Select type of block
while
(default) | do-while
Select type of block.
while
The While Iterator block has two inputs, a
cond
(logical condition) input and anIC
(initial logical condition) input. The source of theIC
signal must be external to the While Iterator Subsystem block.At the beginning of each time step:
If the
IC
input is true (value not equal to0
), the blocks in the subsystem repeat execution while thecond
input is true. This process continues during a time step as long as thecond
input is true and the number of iterations is less than or equal to the Maximum number of iterations.If the
IC
input is false, the While Iterator block does not execute the contents of the subsystem.
do-while
The While Iterator block has one input, the
cond
(while condition) input.At each time step, the blocks in the subsystem repeat execution while the
cond
input is true (value not equal to0
). This process continues as long as thecond
input is true and the number of iterations is less than or equal to the Maximum number of iterations.
Programmatic Use
Block Parameter:
WhileBlockType |
Type: character vector |
Values:
'while' |
'do-while' |
Default:
'while' |
States when starting — Select block states between time steps
held
(default) | reset
Select how to handle block states between time steps.
held
Hold block states between time steps. Block state values persist across time steps.
reset
Reset block states to their initial values at the beginning of each time step and before the first iteration loop.
Programmatic Use
Block Parameter:
ResetStates |
Type: character vector |
Values:
'held' | 'reset' |
Default:
'held' |
Show iteration number port — Control display of output port
off
| on
Control display of output port for signal with number of block executions.
The value of the signal from this port starts at
and is incremented by
1
1
for each succeeding iteration.
- off
Remove output port.
- on
Display output port for signal with iteration number.
Dependencies
Selecting this parameter enables the Output data type parameter.
Programmatic Use
Block Parameter:
ShowIterationPort |
Type: character vector |
Values:
'off' | 'on' |
Default:
'off' |
Output data type — Select output data type for current iteration number
int32
(default) | uint32
| int16
| uint16
| int8
| uint8
| double
Select output data type for iteration number signal. The value of this
signal is the number of iterations during a time step and the total number
of iterations at the end of a time step. The maximum allowable value for the
signal is determined by the Output data type parameter.
For example, if you set Output data type as
int8
, the maximum allowable value for the
signal is 27-1. However, if you set
Output data type as
uint32
or double
,
the maximum allowable value for the signal is restricted to the maximum
positive value for signed 32-bit integer (int32
). For
more information about range of values for different integer classes, see
Integers.
int32
Signed 32-bit integer.
uint32
Unsigned 32-bit integer.
int16
Signed 16-bit integer.
uint16
unsigned 16-bit integer.
int8
Signed 8-bit integer.
uint8
Unsigned 8-bit integer.
double
Double-precision floating point.
Dependencies
Select the Show iteration number port check box to enable this parameter.
Programmatic Use
Block Parameter:
OutputDataType |
Type: character vector |
Value:
'int32' | 'unt32' |
'int16' |
'uint16' |'int8' |
'uint8' |
'double' |
Default:
'int32' |
Version History
Introduced before R2006aR2024b: Add signal breakpoints and port value labels to iteration number outputs in iterator subsystems
You can now pause a simulation on a particular iteration of an iterator subsystem by adding signal breakpoints to signals produced by:
Iteration number output ports of While Iterator blocks inside While Iterator Subsystem blocks
Iterator value output ports of For Iterator blocks inside For Iterator Subsystem blocks
Partition index output ports of For Each blocks inside For Each Subsystem blocks
In previous releases, you could add a breakpoint in these locations, but the breakpoints did not pause the simulation and appeared as invalid in the block diagram.
Port value labels at the same locations now display the iteration number. In previous releases, port value labels at these locations showed inaccessible
.
For an example, see Debug Simulation of Iterator Subsystem.
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