MATLAB: Best method to define constants used by several functions

define constantMATLABmatlab function

I am implementing a model in MATLAB that relies on several functions. All of these functions are dependent on the same set of constants, which currently are defined explicitly in each function (these are all in different m-files). My aim is to run the model several times with different values for the constants, and I'm looking for an easy way to adjust these constants without having to edit all individual functions. I think this may be done using global variables or by defining named constants, but as I've never used any of these methods before I don't know which approach is best or if there is an ever better way to do it.

Edit: One of the functions must remain a single-variable function, and the constants can thus not be passed along as input parameters.

Best Answer

Change your functions to allow the constants to be passed as extra parameters, possibly as one parameter vector that can then be assigned to the individual variables in each of your functions.

I advise avoiding global variables at all costs. They can be inadvertently changed, and debugging code that uses global variables can be difficult.

Related Solutions

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.

MATLAB: How to implement an array of function handles that takes a struct as input and calculates the function value for each function handle

Hello Carolin, you can evaluate functions in a loop:

>> values = zeros(1,length(test));
>> for k = 1:length(test)
       values(k) = test{k}(input_variables,constants);
   end
>> values
values =
    6.0000    3.1416

or using cellfun():

>> values = cellfun(@(F)F(input_variables,constants),test)
values =
    6.0000    3.1416

cellfun looks more compact, but it is often harder to read and modify, especially when you are going back to the piece of code after a while.

Best Answer

Related Solutions

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

MATLAB: How to implement an array of function handles that takes a struct as input and calculates the function value for each function handle

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