MATLAB: Global variables (not sure if it’s the case or not)

global variable

Hi!

I have some numbers defined in the main script whose values are constant during all the simulation.

During the execution of the main I call several functions which take as input some variables and the same numbers defined before and as output some results, the problem is that passing all the numbers as parameters to the functions is quite annoying. Is there a way to bypass this? I tried with some global variables but it doesn't seem to work, I might have made some mistakes with declarations…

For Example (with only one number but I have many of them):

offset = 1;
result = myFunc(3)
%%%%%
function res = myFunc(val)
res = val + offset;

Best Answer

One idea is to use structs. Put all your variables under this struct and you'd need to pass only this struct. For example,

Param.offset = 1;
result = myFun(3,Param)
%%%%%
function res = myFunc(val,param)
res = val + param.offset;

I'd prefer this method than using globals.

link: https://www.mathworks.com/help/matlab/ref/struct.html

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MATLAB: Using the persistent function

A persistent variable is local to one function and one function only. It cannot be shared with another function. It just means that the variable value is preserved between calls to the function.

A global variable is common to all workspaces (as long as each workspace declares the variable explicitly as global). global variables are extremely discouraged though. It is usually an indication of shoddy coding which in the long term will lead to extremely hard to locate bugs.

The standard way to share data between functions is to pass the return value(s) of one function as input argument(s) of the other.

MATLAB: How to make a constant global so all packages files use it

As Stephen has explained already, passing variables as arguments is the best practice.

If you have really good reasons to define a constant globally, do not use global, but prefer a dedicated function, which provides the values as struct:

function C = myPackageConstants()
C.g  = 9.81;
C.pi = 3.14159265;
C.VolumeOfHeidelbergBarrel = 221716;  % liter

Then call this from all function as:

C = myPackageConstants;

This is less clear than using arguments. If it is called very often, it might matter that it has a certain runtime overhead. But in opposite to globals, you can be sure that the values are not modified anywhere, such that debugging gets horrible.

Best Answer

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MATLAB: Using the persistent function

MATLAB: How to make a constant global so all packages files use it

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