How to check if a matrix has already been created?

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.

[Adam]

The obvious solution would be to create a class then this could simply be a property of the class and you can set it or update it when you choose and it will always be available to all functions of the class. If you are not familiar with Matlab OOP though this may be too much work.

[Gabor]

Does not work at R2017a

returns

if(exist matrix == false)

↑

Error: Unexpected MATLAB expression.

This is the correct way:

if(exist ('matrix') == false)

%create matrix

else

%do nothing

Answer 1

[Jan]

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

[Matthew Plummer]

Thanks for the help I have included my code below implementing this. If it is empty I will create it with size 1x1 with value 0 then carry out my comparision in the next loop to populate this matrix.

function maxSplit(improvementValue  
  persistent improvementStorage
    if(isempty(improvementStorage))
      disp('Improvement storage is not initialized');
      improvementStorage = zeros(1);
    end

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