Call function for all elements in an array

Question

Let\'s say I have a function, like:

function [result] = Square( x )
    result = x * x;
end

And I have an array like the following,

Answer 1

I am going to assume that you will not be doing something as simple as a square operation and what you are trying to do is not already vectorised in MATLAB.

It is better to call the function once, and do the loop in the function. As the number of elements increase, you will notice significant increase in operation time.

Let our functions be:

function result = getSquare(x)
    result = x*x; % I did not use .* on purpose
end

function result = getSquareVec(x)
result = zeros(1,numel(x));
    for idx = 1:numel(x)
        result(:,idx) = x(idx)*x(idx);
    end
end

And let's call them from a script:

y = 1:10000;
tic;
for idx = 1:numel(y)
    res = getSquare(y(idx));
end
toc

tic;
    res = getSquareVec(y);
toc

I ran the code a couple of times and turns out calling the function only once is at least twice as fast.

Elapsed time is 0.020524 seconds.
Elapsed time is 0.008560 seconds.

Elapsed time is 0.019019 seconds.
Elapsed time is 0.007661 seconds.

Elapsed time is 0.022532 seconds.
Elapsed time is 0.006731 seconds.

Elapsed time is 0.023051 seconds.
Elapsed time is 0.005951 seconds.