GNU Octave method to operate on each item in a matrix. octave "arrayfun(...)" example

Question

In GNU Octave version 3.4.3, I am having trouble applying a custom function to operate on each item/element in a matrix.

I have a (2,3) matrix that looks like:

mymatrix = [1,2,3;4,5,6];  mymatrix     1   2   3    4   5   6 

I want to use each element of the matrix as an input, and run a custom function against it, and have the output of the function replace the content of mymatrix item by item.

Answer 1

arrayfun works well for this:

arrayfun(@(x) 1/(1+e^(-x)), [0, 1; 2, 3]) 

Output:

ans =     0.50000   0.73106    0.88080   0.95257 

This basically runs function 1/(1+e^(-x)) on each element of the matrix/vector.

Answer 2

Alternatively you can use the element-wise operators like the following (note the dot prefix):

• .+
• .-
• ./
• e.^

For example

mymatrix = 1 ./ (1 .+ e.^(-mymatrix));