MATLAB: How to check if a matrix has already been created

Question

I have a function that will be looped through as the functions call each other i.e. function1->function2->function3->function1 etc.

In one of these functions I want to create a matrix that will store a variable for comparison, however this matrix should be retained during all cycles of the program therefore I only want to create this matrix once.

See pseudocode below for what I want to achieve.

if(exist matrix == false)
%create matrix
else
%do nothing

The use of this is to store an improvement value for splitting a data set. See below:

if(improvementValue > improvementStorage(1,1))
    improvementStorage(1,1)= improvementValue;
end

(improvementStorage being the matrix I want to create on the first iteration only.)

Any help on how to create this matrix once and not overwriting it with each program iteration would be appreciated.

Answer 1

You can either define a variable which is included in the inputs and outputs of all functions. Then you have full control from anywhere.

Or you can use a persistent variable in one function:

function out = myFunc(In)
persistent M
if isempty(M)
  disp('M is not initialized');
end
M = rand(2);
end