How to compile a Simulink file?

Dear reader,

I am trying to get an insight into the best practice towards writing matlab code that can be used with Simulink. In other words, I would like to be able to compile in Simulink, this toy example scheme:

where inside the Matlab embedded function I call:

y = select1([1 0 2 0 3]);

The function select1.m identifies the zeros inside a vector and returns their position:

function x = select1(y)

x = [];

for i=find(y==0)
    x = [x i];
end

Now, once I run the Simulink scheme it gives errors, complaining about select1.m There are 2 main problems here:

1. the usage of variable size vectors (namely x)
2. the for-loop is written in a way that coder cannot interpret it

In particular, my question is the following: what is the best practice towards (re)writing this simple piece of code select1.m such that the Simulink scheme described above can compile, without generating errors?

Thank you

Answer 1

[Walter Roberson]

Try something like

ind = find(y==0);
x = zeros(size(ind));
for k = 1 : length(ind)
  x(k) = ind(k);
end

This could probably be shortened to

x = find(y==0);

but you did say it was a toy example so I will presume that the purpose is to produce a variable-length output iteratively.

Beyond that see http://www.mathworks.com/help/fixedpoint/ug/defining-variable-size-data-for-code-generation.html