load global variable from startup.m

Is it possible to dfine a global variable using ...\Documents\MATLAB\startup.m? I would like to define frequently used variables and have them available after launching MATLAB.

[Adam]

I just define a class containing constants I want easy access to, e.g.

classdef Constants
	properties( Constant, Access = public )
            % File size stuff
            OneGigabyte = 1073741824;
            OneMegabyte = 1048576;    
            OneKilobyte = 1024;
            
            % Degree/Radian conversion
            RadiansToDegrees = 57.2957795130823;
            DegreesToRadians = 0.0174532925199433;
            
            % Frequency analysis
            Nyquist = 0.5;
  
            ...
	end
end

I don't define many so I'm happy enough with them all in one file, but if I had loads I would likely define numerous classes, e.g. FileConstants, FrequencyConstants, etc, etc.

I can just call these anywhere in code as e.g.

myArray = rand( 300, 400, 500 );
arraySizeGB = size( myArray ) * 8 / Constants.OneGigabyte;

etc.

Most things I have defined in classes that they are relevant to, but these are just the odds and ends that are leftover in my case that I stick in one easy-access file. Most of them I rarely use, except those file size ones, almost exclusively for quick command line checking how much memory I would need for something or other.

Answer 1

[Nicolas B.]

I clearly don't recommend your to do so. Instead, I would add some functions in your standard Matlab path which returns your constants. Then, it will be accessible from any script/function/class you (and only you or the persons with your library) will create.

Example:

you have a variable which gives you the 0°K in °C:

function k0 = zeroDegKelvin()
    k0 = -273.15;
end

If you do so. I would recommend you to create a toolbox from your function lists or to use git/svn/... to have them on a server. That way, you can easily install your functions on another pc or after a installation refresh of yours.