The model `sf_varsize_example`

shows how MATLAB^{®} functions
in Stateflow^{®} charts exchange variable-size data with other charts
and blocks in the model. To open the model, click `sf_varsize_example`

.

In this model, one Stateflow chart, `VarSizeSignalSource`

,
uses temporal logic to generate a variable-size signal. A second chart, `size_based_processing`

,
computes the output based on the size of the signal generated by the
first chart:

The `VarSizeSignalSource`

chart works like
a source block. It has no input and one variable-size output `y`

:

For variable-size outputs, you must explicitly specify the size
and upper bound for each dimension. In this case, `y`

is
a vector where the first dimension is assumed to be fixed at size
1 and the second dimension is variable with an upper bound of 16.

This chart uses temporal logic to transition between three states, each generating a different size output:

No states or transitions can read from or write to variable-size
data. Therefore, `y`

does not appear in any state
actions or transition logic. All computations involving variable-size
data must occur in MATLAB functions in the chart.

MATLAB functions access variable-size, chart-level data
directly. You do not pass the data as inputs or outputs to the functions.
In this chart, the `generateOutput`

function adds
a different number of elements to the variable-size output `y`

,
based on how the active state calls it. The function constructs the
variable-size vector from a number sequence, then outputs the transpose
of the result:

function generateOutput(len) %#codegen assert(len<=16); y = (1:len)';

MATLAB functions must be able to determine the upper bounds
of variable-size data at compile time. In this case, however, the
upper bound is `len`

, an input for which the model
computes the value at run time. To provide this information, the `assert`

function
specifies an explicit upper bound for `len`

, one
that matches the upper bound for chart output `y`

.

If you do not include the assert statement, you get a compilation error:

Computed maximum size is not bounded. Static memory allocation requires all sizes to be bounded. The computed size is [1 x :?].

The `size_based_processing`

chart computes
a variable-size output based on the value of a variable-size input:

Input

`u`

is the variable-size signal generated by the`VarSizeSignalSource`

chart:Output

`y`

is a variable-size signal whose size depends on whether`u`

is a scalar or vector:The chart uses three MATLAB functions to evaluate the size of input

`u`

and generate an associated output`y`

:As in the chart

`VarSizeSignalSource`

, variable-size data does not appear in state actions or transition logic. Instead, states call MATLAB functions to compute the variable-size output. Transitions call a MATLAB function in a conditional statement to evaluate the variable-size input.

This function tests whether chart input `u`

,
the signal generated by chart `VarSizeSignalSource`

,
is a scalar or vector value:

function isScalar = is_scalar_input %#codegen isScalar = length(u)==1;

If input `u`

is a vector, this function outputs
the sine of each of its values:

function compute_output %#codegen y = sin(u);

If input `u`

is a scalar, this function outputs
a value of zero:

function reset_output %#codegen y = 0;

Open the model:

sf_varsize_example

Open the chart

`VarSizeSignalSource`

, but keep the Simulink^{®}display blocks in view.Start simulation from the chart.

The display blocks periodically show 1, 8, and 16 values from the variable-size vector.

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