How do I make a section of a function runs only one time?

I am running a fimincon algorithm to minimize this function. But the marked part takes a long time to run, and when apply to fmincon, the code takes forever to run. Is there a way to make this section run only once?

Answer 1

[DGM]

One way might be to use persistent variables.

function out = myfunction(a,b,c)
    persistent S data_mdl
    if isempty(S) | isempty(data_mdl)
        % do code to get S and data_mdl
    end
    % do other code
end

There are probably better ways.

You're also doing combine_sess(S) twice, once in the setup, and once in the squared distance line. I don't see why you can't replace the second instance with data. In that case, you wouldn't need to keep S anymore. You'd only need data and data_mdl.

[Yifan Zhang]

Hi, so i did the persistent command. But as I ran fmincon, it shows 'Unrecognized function or variable 'data'.' Not sure what's going wrong.

[DGM]

Ah sorry. If you make that substitution, you'll have to set data and data_mdl as persistent instead of S and data_mdl. Whichever variables you need to persist between function calls are the ones that need to be specified.

persistent data data_mdl
if isempty(data) | isempty(data_mdl)

Answer 2

[Stephen23]

The MATLAB approach is to move that code outside of the function and parameterize the function call:

https://www.mathworks.com/help/matlab/math/parameterizing-functions.html

The simplest is to use an anonymous function, something like this:

data = slow importing and other call-once code here
..
fnh = @(x) objfun(x,data); % <- you need this!
out = fmincon(fnh,..)

This is much easler than using persistent variables (which require clearing before running).