persistent variable from previous run is not deleted during a new run of my .m file

Here is how my program is structured in a .m file:

clear function_name;
clear all;
clc; 
close all; 
...
    for i = ...
        ...
        ret_val = function_name(...)  # function call
        ...
    end
...

function ret_val = function_name(...)
    ...
    persistent persistent_var
    ...
    if( isempty(persistent_var) )  
        persistent_var = 1
    end
    ...
end

I rubn the program loading this m file in editor and pressing F5. The first run works as expected but on the subsequent runs persistent_var is not empty, and seems to be retained from the previous run. Only way sure fire way I have found to delete it is by executing "clear all" in the command window before running my .m file. Nothing else deletes persistent_var from the previous run.

1. What is the proper way to delete persistent variables between program executions? I need this variable to not exist during the first call to the functon in my program.
2. What is the proper way to do this in matlab? I need somethign equivalent to C static variables, so that I can detect the first call to function_name() during my program run and perform a specific task inside it, which should not be performed during later calls to the function.

Answer 1

[Stephen23]

MATLAB is not C. The tidiest way to avoid that ugliness is to use nested functions:

https://www.mathworks.com/help/matlab/matlab_prog/nested-functions.html

Using nested function avoids this whole problem by design, rather than attempting to "fix" it afterwards with ever larger hammers.

function mainfun()
some_var = 1;
...
for ii = 1:Inf
    ...
    ret_val = nested_fun(..);
    ...
end
...
    function ret_val = nested_fun(...)
        ...
        some_var
        ...
    end
end

Answer 2

[Torsten]

Using two .m-files instead of only one script seems to solve the problem according to

https://uk.mathworks.com/matlabcentral/answers/2142431-how-can-i-use-the-clear-function-to-clear-persistent-variables-in-local-or-nested-functions-in-mat