Call function for all elements in an array

function, indexing, matlab

Solution

For the example you give:

y = x.^2;   % or
y = x.*x;

in which `.*` and `.^` are the element-wise versions of `*` and `^`. This is the simplest, fastest way there is.

More general:

y = arrayfun(@Square, x);

which can be elegant, but it's usually pretty slow compared to

y = zeros(size(x));
for ii = 1:numel(x)
    y(ii) = Square(x(ii)); end

I'd actually advise to stay away from `arrayfun` until profiling has showed that it is faster than a plain loop. Which will be seldom, if ever.

In new Matlab versions (R2008 and up), the JIT accelerates loops so effectively that things like `arrayfun` might actually disappear in a future release.

As an aside: note that I've used `ii` instead of `i` as the loop variable. In Matlab, `i` and `j` are built-in names for the imaginary unit. If you use it as a variable name, you'll lose some performance due to the necessary name resolution required. Using anything other than `i` or `j` will prevent that.

Problem

Let's say I have a function, like: ``` function [result] = Square( x ) result = x * x; end ``` And I have an array like the following, ``` x = 0:0.1:1; ``` I want to have an `y` array, which stores the squares of `x`'s using my `Square` function. Sure, one way would be the following, ``` y = zeros(1,10); for i = 1:10 y(i) = Square(x(i)); end ``` However, I guess there should be a more elegant way of doing it. I tried some of my insights and made some search, however couldn't find any solution. Any suggestions?

Original source