MATLAB: Location of the “end” statement of the main function in a m. file

endlocal functionmain function

Hello,

could someone write what is the difference between possible location of the "end" statement of the main function: before first local function vs end of a file? What is the difference?

For example: first vs. second case in this answer.

Thank you!

Marek

Best Answer

"before first local function"

any functions defined after the main function are local functions:

https://www.mathworks.com/help/matlab/matlab_prog/local-functions.html

"vs end of a file?"

any functions defined within the main function are nested functions:

https://www.mathworks.com/help/matlab/matlab_prog/nested-functions.html

These can be combined too, e.g.:

function mymain()
... code
    function mynest()
        ... code
    end % mynest()
end % mymain()
function mylocal()
... code
end % mylocal()

Nested functions have access to the parent function's workspace. Local functions do not.

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MATLAB: How to save functions or sub functions in matlab

It is not clear from your explanation where you are defining the function, but I can see two main possibilities which would generate that error (or a similar error):

Trying to define a function in the command window: this is not allowed in MATLAB, all functions must be saved in a file (except for anonymous functions).
Trying to define a function inside a script: only MATLAB versions from R2016B+ support functions defined in scripts. You need to read the documentation carefully for your version, not the online help (which is for the most recent version): for your MATLAB version it is not possible to define a function inside a script.

In practice if you want to define a function then do NOT have any code outside of any function declaration, e.g. this needs to be the entire file contents:

function [m,s] = stat(x)
n = length(x);
m = sum(x)/n;
s = sqrt(sum((x-m).^2/n));
end

You can add local functions to the same file, but NO CODE outside of those functions. Save the function as a file stat.m (you should use the same name as the function itself). Then it will work.

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Yes, you could write an anonymous function as your nonlinear constraint function as long as your constraints are simple enough.

f = @(x) deal(x.^2, x.^3);
[a, b] = f(1:5)

However, I'm not sure that's going to achieve your end goal. "I need it since some of the constants which appear in my constraint function should be computed by other code and are not simply numbers which I can fix before running my code." In that case you may want to consider nested functions. Define the shared variable in the main function and nest the nonlinear constraint and whatever other functions need access to that shared variable inside the main function. Adapting one of the examples on that page to illustrate what I mean:

function y = findzero(b,c,x0)
t = 0;
[y, ~, ~, out] = fzero(@poly,x0);
fprintf('FZERO called poly %d times according to t.\n', t);
fprintf('FZERO called poly %d times according to out.\n',out.funcCount);
     function y = poly(x)
     y = x^3 + b*x + c;
     t = t + 1;
     fprintf('t = %d, x = %f, y = %f\n', t, x, y);
     end
  end

The poly function nested inside findzero has access to the b, c, and t variables defined inside findzero. It only reads from b and c, but it both reads from and writes to t.

Best Answer

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