MATLAB: how to apply function componentwise

Question

Say I have a function calculateStuff(x) that takes in a scalar as parameter and returns a scalar.

Say I have a vector X and I want to apply calculateStuff on every component in X, and get a vector of the results in return and store it in a new vector Y.

Clearly Y=calculateStuff(X) is illegal, is there a way I can do this besides looping?

Answer 1

You have three options:

1. modify calculateStuff so that it can take arrays and return arrays
2. write a loop
3. use arrayfun to hide the loop: Y = arrayfun(@calculateStuff,X)

Answer 2

Most Matlab operations will let you input a matrix and return a matrix. You should be able to re-write calculateStuff() to take a matrix and return a matrix. That is generally MUCH faster than using a for loop. Loops in Matlab are very expensive time-wise.

The sorts of things you need to look at are "dot" versions of normal operations. For example instead of

y = z * x;

do

y = z .* x;

The first will do a matrix multiplication, which is probably not what you want when vectorizing code. The second does an element-by-element multiplication of z and x.

See here and search for "The dot operations".