Index and Assign Values to Stateflow Structures

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This example shows how to access and modify the contents of a Stateflow® structure. Stateflow structures enable you to bundle data of different sizes and types together into a single Simulink.Bus object. Using dot notation and numeric indices, you can access and modify the contents of a Stateflow structure. For more information, see Access Bus Signals Through Stateflow Structures

Index Substructures and Fields

To index substructures and fields of Stateflow structures, use dot notation. The first part of a name identifies the parent object. Subsequent parts identify the children along a hierarchical path. When the parent is a structure, its children are individual fields or fields that contain other structures (also called substructures). The names of the fields of a Stateflow structure match the names of the elements of the Simulink.Bus object that defines the structure.

For example, the chart in this model contains an input structure (in), an output structure (out), and two local structures (localbus and subbus).

  • The chart defines the input structure in, the output structure out, and the local structure localbus by using the Simulink.Bus object BusObject. These structures have four fields: sb, a, b, and c. The field sb is a substructure defined from the Simulink.Bus object SubBus.

  • The chart defines the local structure subbus by using the Simulink.Bus object SubBus. This structure has one field called ele.

This list illustrates how the Stateflow chart resolves symbols in dot notation for indexing the fields of these structures:

  • in.c — Field c of input structure in.

  • out.sb — Substructure sb of output structure out.

  • in.a(1) — First value of the vector field a of input structure in.

  • subbus.ele(2,2) — Value in the second row, second column of field ele of local structure subbus.

  • in.sb.ele(3,4) — Value in the third row, fourth column of field ele of substructure in.sb.

Assign Values to Structures and Fields

You can assign values to any Stateflow structure, substructure, or a field of a structure with a scope different from Input.

  • To assign one structure to another structure, define both structures from the same Simulink.Bus object in the base workspace.

  • To assign one structure to a substructure of a different structure (or the other way around), define the structure and substructure from the same Simulink.Bus object.

  • To assign a field of one structure to a field of another structure, the fields must have the same type and size. You can define the Stateflow structures from different Simulink.Bus objects.

This list presents valid and invalid structure assignments based on the structure specifications for this example:

  • in = localbus; — Invalid. You cannot write to input structures.

  • out = localbus; — Valid. Both out and localbus are defined from the same Simulink.Bus object BusObject.

  • subbus = in; — Invalid. The structures subbus and in are defined from different Simulink.Bus objects.

  • subbus = in.sb; — Valid. The structure subbus and the substructure in.sb are defined from the same Simulink.Bus object SubBus.

  • in.sb = subbus; — Invalid. You cannot write to substructures of input structures.

  • out.sb = subbus; — Valid. The substructure out.sb and the structure subbus are defined from the same Simulink.Bus object SubBus.

  • in.c = out.c; — Invalid. You cannot write to fields of input structures.

  • out.sb.ele = subbus.ele; — Valid. The field out.sb.ele has the same type and size as the field subbus.ele (3-by-3 matrices of type int8).

  • localbus.a(1) = in.c; — Valid. The value localbus.a(1) has the same type and size as the field in.c (scalars of type double).

For instance, in the entry action for state A, the chart calls the functions abc2sb and sb2abc and stores the results in the local structures localbus and subbus. Then, the chart writes to the output structure out by combining the values of the local structures localbus and subbus.

The graphical function abc2sb takes a structure of type BusObject and returns a structure of type SubBus. The function combines the values of the fields a, b, and c from its input and rearranges them in a 3-by-3 matrix of type int8. Then, the function stores this matrix as the field ele of the output structure.

The MATLAB® function sb2abc takes a structure of type SubBus and returns a structure of type BusObject. The function decomposes the value of the field ele from its input into three components: a vector, a 3-by-2 matrix, and a scalar. The function stores these components in a local MATLAB struct Y that has the same structure as the Simulink.Bus object BusObject. Then, the function assigns the value of the MATLAB struct Y to the output structure y.

function y = sb2abc(u)

% extract data from input structure

E = int8(magic(3));
A = double(u.ele(1:2,1));
B = uint8(u.ele(:,2:3));
C = double(u.ele(3,1));

% create local structure

X = struct('ele',E);
Y = struct('sb',X,'a',A,'b',B,'c',C);

% assign value to output structure

y = Y;
end

Run the Simulation

When you simulate the example, the chart uses the values of the field sb of the input bus to populate the fields a, b, c of the output bus. The chart also uses the values of the fields a, b, c of the input bus to populate the field sb of the output bus.

See Also

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Related Topics

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