Why do I receive Undefined function errors for HEAVISIDE function when I try to compile it in a FIT object in MATLAB 7.8 (R2009a)?

I am computing a FIT using the HEAVISIDE function. This works fine inside MATLAB but fails with the following error in my compiled application.

 ??? Error using ==> fittype.fittype>fittype.fittype at 466 

 Expression a.*heaviside(b-x).*(b-x) is not a valid MATLAB expression, 

has non-scalar coefficients, or cannot be evaluated: 

 Error in fittype expression ==> a.*heaviside(b-x).*(b-x) 

 ??? Undefined function or method 'heaviside' for input arguments of type 

 'double'.

Answer 1

[MathWorks Support Team]

The HEAVISIDE function is a function present in the Symbolic Math Toolbox. The Symbolic Math Toolbox functions cannot be compiled using the MATLAB Compiler.

http://www.mathworks.com/products/ineligible_programs/

To workaround this issue, you can write your own heaviside function as shown below:

function Y = heaviside1(X)

%HEAVISIDE    Step function.

Y = zeros(size(X));

Y(X > 0) = 1;

Y(X == 0) = .5;

end

Now, you can use the above custom heaviside function in your MATLAB code as follows:

function my_fit

% Create a fit

x = [1:10]';

y = x*0.25;

z = [-0.5:0.1:0.5];

% Create a FIT

cfit = fit(x,y,'a.*heaviside1(b-x).*(b-x)'); % using custom heaviside1

cfit

d = cfit(z);

plot(x,y,'*k',z,d,'.');

You can then compile this code into a standalone executable using the following command:

mcc -m my_fit.m -a heaviside1.m