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Compute Output Based on Size of Input Signal

This example shows how to modify the size of output data in a Stateflow® chart during simulation.

In this model, a Stateflow chart called VarSizeSignalSource uses temporal logic to generate a variable-size signal. A second chart called SizeBasedProcessing computes the output based on the size of the signal generated by the first chart. Display blocks show the values and size of the signals.

Generate Variable-Size Output Data

The Stateflow chart VarSizeSignalSource uses MATLAB® as the action language. The temporal logic in this chart triggers the transitions between four states. Each state generates an output value with a different size: a scalar, a two-element column vector, a four-element row vector, and a 2-by-4 matrix.

The chart behaves 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 bounds for each dimension. In this case, the Variable size property for y is enabled and its Size property is set to [2 4], the maximum size for the signal.

In charts that use MATLAB as the action language, state and transition actions can read and write directly to variable-size data. For example, the entry actions of the states in this chart explicitly compute the value of y.

Process Variable-Size Input Data

The Stateflow chart SizeBasedProcessing uses C as the action language. These charts can exchange variable-size data with other charts and blocks in the model. However, state and transition actions in C charts cannot read from or write to variable-size data directly. All computations involving variable-size data must occur in MATLAB functions, Simulink® functions, and MATLAB truth tables in the chart.

This chart has two variable-size data objects:

  • Input u is the variable-size signal generated by the VarSizeSignalSource chart. The Size property for u is set to -1 to indicate that this input inherits its size from the Simulink model. Note that only inputs to C charts can inherit their size.

  • Output y is a variable-size signal whose size and value depends on whether u is a scalar, a vector, or a matrix. The Size property for u is set to [2 4], the maximum size for the signal.

Because this chart uses C as the action language, the names of the variable-size data do not appear in the state actions or transition logic. Instead, the transition logic in the chart calls the MATLAB function readInputSize to determine the size of the input u. Similarly, the actions in the states call the MATLAB function computeOutput to produce values of various size for the variable-size output y. Because MATLAB functions can access chart-level data directly, you do not have to pass the variable-size data as inputs or outputs to these functions.

Determine Size of Input

The MATLAB function isScalarInput determines the size of the chart input u. This signal, which is generated by chart VarSizeSignalSource, can be a scalar, a 2-by-1 column vector, a 1-by-4 row vector, or a 2-by-4 matrix. The function stores the dimensions of u as the chart-level output z.

function readInputSize
%#codegen
z = size(u);
end

Produce Variable-Size Output

The MATLAB function computeOutput computes the value of the chart output y based on the size and value of the chart input u.

  • If u is a scalar, the function assigns to y a scalar value of zero.

  • If u is a column vector, the function computes of the sine of each of its elements and stores them in y.

  • If u is a row vector, the function computes of the cosine of each of its elements and stores them in y.

  • If u is a matrix, the function computes of the square root of each of its elements and stores them in y.

In each case, the value of the output y has the same size as the input u.

function computeOutput(key)
%#codegen
switch key
    case 0 % scalar
        y = 0;
    case 1 % column vector
        y = sin(u);
    case 2 % row vector
        y = cos(u);
    case 3 % matrix
        y = sqrt(u);
end
end

Simulate the Model

The tabs located above the Explorer Bar enable you to switch between the Simulink model and the two Stateflow charts. During simulation:

  • The chart animations show the active state for each chart cycling between the Scalar, ColumnVector, RowVector, and VectorPartial, and Matrix states.

  • In the Simulink model, the display blocks Signal Source and Processed Signal periodically show between one and eight values for the variable-size signals.

  • The display block Size of Signal and the Scope block show the number of rows and columns in the variable-size signals.

See Also

Related Topics