Perfect use to global variables across functions

I am working with Monte Carlo Simulation approach, some constants have been fixed at the top of the main script also data is simulated in the main script. I created some functions script files work over estimation and computations. To avoid calling the variables that have been created or fixed in the main file I defined them as global.

Matlab gives me the following warning message, can anybody advise??

Warning: The value of local variables may have been changed to match the globals. Future versions of MATLAB will require that you declare a variable to be global before you use that variable.

[John D'Errico]

Advise? Um, don't use globals? They are a good way to create bad code, difficult as anything to debug.

Instead learn to pass your data between functions. You can collect it all into a single struct if there are too many variables.

Sorry, globals are just a crutch for those who choose not to learn better methods.

[Stephen23]

"can anybody advise ??"

Yes! Avoid using global variables. Pass your data properly as input/output arguments, using nested functions, etc., as recommended in the MATLAB documentation:

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

For example it is easy to parameterize functions:

https://www.mathworks.com/help/matlab/math/parameterizing-functions.html

"To avoid calling the variables that have been created or fixed in the main file I defined them as global."

And that is the bad code design decision right there.

https://blogs.mathworks.com/videos/2010/03/08/top-10-matlab-code-practices-that-make-me-cry/

[Niveen El Zayat]

John and Stephen, Thanks a lot for your advise. Comment on "You can collect it all into a single struct"

In fact that was the idea I was searching for because I used to do so with STATA when I repeated code over same variables, but I failed to find it in Matlab, I think now I can find it. Lot of thanks

[Stephen23]

"...because I used to do so with STATA when I repeated code over same variables..."

Different languages do things in different ways. If you want to write good code and waste less of your time, then you really need to learn the features of each language. You might be interested to read this:

https://www.mathworks.com/matlabcentral/answers/320774-looping-over-a-set-of-names-and-creating-a-set-of-variables

Answer 1

[Walter Roberson]

That particular message occurs when you have a global statement for a variable name that you had already assigned a value to inside the function. For example

G = 5
global G

would generate the message, because the global G that is activated might not have value 5. The above does not mean to initialize G to 5 and then to "promote" G to be global: it means to create a local variable named G with value 5 and then to remove the variable from the workspace and make G refer to the existing value of the global variable G.

No offence intended, but people who do not know this about global variables should probably not be using global variables. Global variables are easy to make mistakes with, and should be avoided.