matlab local static variable

Question

In order to test an algorithm in different scenarios, in need to iteratively call a matlab function alg.m.

The bottleneck in alg.m is something like:

load large5Dmatrix.mat
small2Dmatrix=large5Dmatrix(:,:,i,j,k)  % i,j and k change at every call of alg.m
clear large5Dmatrix

In order to speed up my tests, i would like to have large5Dmatrix loaded only at the first call of alg.m, and valid for future calls, possibly only within the scope of alg.m

Is there a way to acheve this in matlab other then setting large5Dmatrix as global?

Can you think of a better way to work with this large matrix of constant values within alg.m?

Answer 1

You can use persistent for static local variables:

function myfun(myargs)
    persistent large5Dmatrix
    if isempty(large5Dmatrix)
        load large5Dmatrix.mat;
    end

    small2Dmatrix=large5Dmatrix(:,:,i,j,k)  % i,j and k change at every call of alg.m
    % ... 
end

but since you're not changing large5Dmatrix, @High Performance Mark answer is better suited and has no computational implications. Unless you really, really don't want large5Dmatrix in the scope of the caller.