Using Simulink

Declaring Local Variables Implicitly

You declare variables implicitly in Embedded MATLAB functions by specifying constants and making initial assignments. By default, this type of variable does not persist between function calls. It is recreated for each function call and has no identity or value outside the Embedded MATLAB function. You can, however, make this variable persistent with a persistent statement at the top of the function body before the first use of the variable. For example, to declare the variable abc persistent, enter the following line right after the function header and comments:

• persistent abc;
  

You declare variables implicitly in the function body of Embedded MATLAB functions in the following ways:

• By using constants (for example, 3, 5.7, and so on)

• Constants have the MATLAB type double.

• By declaring variables in an Embedded MATLAB function with a first use in a simple assignment

• The first use of a variable must initialize its value, its type, and its size. For example, the following initial assignments declare variables in an Embedded MATLAB function:

  • a = 14.7; %a is a scalar of type double.
    b = a; %because a is of type double, so is b.
    c = zeros(5,2); %c is a 5-by-2 array of 0 elements of type double.
    d = c; %d is also a 5-by-2 array of 0 elements of type double.
    e = [1 2 3 4 5; 6 7 8 9 0]; % e is a 5-by-2 array of type double.
    

The following rules apply to the use of variables that you declare implicitly in the body of an Embedded MATLAB function:

• Variables that you declare in the body of an Embedded MATLAB function disappear between calls, unless you declare them to be persistent between calls with the persistent statement.
• You cannot set the size of a variable by a first use assignment with indexing.

• In MATLAB, you can declare the size of a variable using indexing. In Embedded MATLAB functions, this is not allowed. For example, the following initial assignment is not allowed in Embedded MATLAB functions:

  • g(3,2) = 14.6; %Not allowed for creating g.
                     %OK for assigning value once created
    

  In MATLAB, the preceding example declares g to be a 3-by-2 array of type double elements, in which the element g(3,2) is 14.6 and all other elements are 0. In Embedded MATLAB functions, this statement is not allowed.

• You can declare variables implicitly with first use typecast functions.

• In the following example code, you declare y and z to be integers with the following initial assignments:

  • x = 15; %Because constants are of type double, so is x.
    y = int16(3); %y is a constant of type int16.
    z = uint8(x); %z is x (double type) cast to uint8.
    

• Variables cannot be resized or cast to a different type once the are created in the function by a first use.

• In the following example, the last two statements each flag an error:

  • x = 2.75 %OK
    y = [1 2; 3 4] %OK
    x = int16(x); %ERROR: cannot recast x
    y = [1 2 3; 4 5 6] %ERROR: cannot resize y
    

Local Variables in Embedded MATLAB Functions

Declaring Local Complex Variables Implicitly

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