## Declare Variable-Size MATLAB Function Block Variables

MATLAB Function blocks support variables that change size during simulation if the
**Support variable-size array** block property is enabled. See Support variable-size arrays. However, only variables
that you specify as variable size can change in size during simulation. Depending on the
scope, you can set variables as variable size by using the **MATLAB Function Block
Editor**, by using the `coder.varsize`

function, or by inheriting
size variability from the connected block signal. For more information about scope, see Scope.

### Output Variables

By default, output variables are not variable size. To specify an output as variable size:

Double-click the MATLAB Function block to open the

**MATLAB Function Block Editor**.Open the

**Symbols**pane and the Property Inspector. In the**Function**tab, click**Edit Data**.In the

**Symbols**pane, select the output variable.In the Property Inspector, in the

**Properties**tab, select the**Variable size**property.In the

**Size**property, specify the size as the upper bound. For example, to specify a 2-by-4 matrix as the largest acceptable size, enter`[2 4]`

. See Customize Variable Sizes.

### Other Scope Types

Input variables inherit size from their attached signals. Therefore, you do not explicitly define input variables as variable size. Input variables can also be unbounded. For more information on creating variable-size signals, see Variable-Size Signal Basics.

If the variable is not an input or output variable, define the variable by using the
`coder.varsize`

function. See Define Variable-Size Data Explicitly by Using coder.varsize.

### Use a Variable-Size Signal in a Filtering Algorithm

This example uses a variable-size vector to store the values of a white noise signal.

The size of the vector can vary at run time because the functions prune the signal values by:

Filtering out signal values that are not unique to within a specified tolerance of each other.

Averaging every two signal values and outputting only the resulting means.

In this model, a Band-Limited White Noise block generates a set of normally distributed random values as the source of a white noise signal. The MATLAB Function block `Filter`

filters out signal values that are not unique to within a specified tolerance of each other. Then, the MATLAB Function block `Average`

outputs the average of a specified number of unique signal values. The Scope blocks display the output from the `Filter`

and `Average`

blocks. Open the model to see the configuration.

**Inspect the Source Signal**

Open the Band-Limited White Noise block to view the properties of the source signal. The size of the **Noise power** parameter defines the size of the array that holds the signal values. This array is a 1-by-9 vector of double values.

**Inspect the Filter MATLAB Function Block**

Open `Filter`

to inspect the filtering function. `Filter`

filters out unique signal values that are not within a tolerance of `0.2`

of each other. The function calls an external MATLAB® function file, `emldemo_uniquetol.m`

, to filter the signal values. The function passes the 1-by-9 vector of white noise signal values as the first argument and the tolerance value as the second argument.

```
function y = uniquify(u)
y = emldemo_uniquetol(u,0.2);
```

Open the MATLAB function file `emldemo_uniquetol.m`

to view the code for the external function, `emldemo_uniquetol`

. `emldemo_uniquetol`

returns the filtered values of `A`

in an output vector `B`

so that `abs(B(i) - B(j)) > tol`

for all `i`

and `j`

.

function B = emldemo_uniquetol(A,tol) %#codegen

A = sort(A); B = A(1); k = 1; for i = 2:length(A) if abs(A(k) - A(i)) > tol B = [B A(i)]; k = i; end end

At each time step, the Band-Limited White Noise block generates a different set of random values for `A`

, and `emldemo_uniquetol`

may produce a different number of output signals in `B`

. Therefore, `y`

must be variable size. In order for `y`

to be variable size, you must enable the **Variable size** property. In this example, **Variable size** is enabled for `y`

. In `Filter`

, open the **Symbols** pane and Property Inspector. In the **Function** tab, click **Edit Data**. In the **Symbols** pane, click `y`

to view the properties in the Property Inspector. For variable-size outputs, you must specify the **Size** property as the maximum-size upper bound. In the example, **Size** is `[1 9]`

.

**Inspect the Average MATLAB Function Block**

`Average`

averages the values filtered by `Filter`

by following these conditions:

If the number of signals is greater than

`1`

and divisible by`2`

, then`Average`

averages every consecutive pair of values.If the number of signals is greater than

`1`

but not divisible by`2`

, then`Average`

drops the first value and averages the remaining consecutive pairs.If there is exactly one signal, then

`Average`

returns the value unchanged.

Open `Average`

to view the code.

```
function y = avg(u)
```

if numel(u) == 1 y = u; else k = numel(u)/2; if k ~= floor(k) u = u(2:numel(u)); end y = emldemo_navg(u,2); end

The `avg`

function calls the external MATLAB function `emldemo_navg`

to calculate the average of every two consecutive signal values.

function B = emldemo_navg(A,n) %#codegen

assert(n>=1 && n<=numel(A));

B = zeros(1,numel(A)/n); k = 1; for i = 1 : numel(A)/n B(i) = mean(A(k + (0:n-1))); k = k + n; end

Both `u`

and `y`

are variable size. You do not need to explicitly define u as variable size, because `u`

is an input. The output `y`

is declared as a variable-size vector because the number of elements varies depending on the size provided by `u`

. Inspect the properties of `y`

to confirm that it is variable size.

**Simulate the Model**

Simulate the model to view the results in each Scope block. `Filter`

outputs a variable number of signal values each time it executes.

`Average`

outputs a variable number of signal values each time it executes. The block returns approximately half the number of the unique values.