Using a Variable between different functions

Hello,

I have this two function. evAlice and evBob were defined in CHSH_ but I need to access themin basis function. But I could not know how can I access to evAlice and evBob in basis fucntion.

function [coin, I] = CHSH_(sigma_x,sigma_z)
    ev1_of_alice = sigma_x;
    ev2_of_alice = sigma_z;
    ev1_of_bob = sigma_x+sigma_z;
    ev2_of_bob = sigma_x-sigma_z;
    evAlice=[sigma_x,sigma_z];
    evBob=[sigma_x+sigma_z,sigma_x-sigma_z];
    ... %function is too long so I just put the relevant part
end
function [basis_mat] = basis(measurement_setting)
    % Choose the correct basis depending on the
    % measurement setting. If you change the observables,
    % these are obtained by diagonalization

    switch measurement_setting
        case evAlice(0)
            basis_mat = [1, 1; 1,-1]/sqrt(2);
        case evAlice(1)
            basis_mat = [1, 0; 0, 1];
        case evBob(0)
            basis_mat = [ 1+sqrt(2), 1-sqrt(2); 1, 1];
        case evBob(1)
            basis_mat = [-1-sqrt(2),-1+sqrt(2); 1, 1];
    end
end

Answer 1

[the cyclist]

You can pass them out of the first function:

function [coin, I, evAlice, evBob] = CHSH_(sigma_x,sigma_z)

and into the second one by calling it like this

basis(measurement_setting, evAlice, evBob)

and defining it as

function [basis_mat] = basis(measurement_setting, evAlice, evBob)

Alternatively, you could define those variables as global in scope, in both functions, but that is generally a bad idea.

[Gözde Üstün]

Thanks I tried it but actually except these function I have 2 function more and basis is the last so when I tried this way I have to add all variables in all fucntion. Instad of that can I use global variable or is this better ?

[the cyclist]

It's really up to you, based on what you think makes the code simpler and easier to understand in the long run.

You might want to google "global variable bad idea matlab" and do a little reading, before you decide. :-)

[Stephen23]

"Instad of that can I use global variable or is this better ?"

Global variables: slower, more buggy, harder to debug, obfuscate the code intent.

Input/output variables: faster, easier to debug, recommended by the MATLAB documentation as "best practice":

https://www.mathworks.com/help/matlab/matlab_prog/share-data-between-workspaces.html

If you have lots of arguments then put them into a structure and pass that.

[Gözde Üstün]

Thank you very very much : -) @the cyclist and @Stephen Cobeldick