Global variables and arguments in matlab which is fastest

Questions

I am using a recursive function in Matlab where some variable are required at each level, these don t change. Though some do change in functions and also need to be reflected in main program.

I d like to know which is best:

• To define variables global in main & function like global in1, in2, out1
• or pass then as arguments to function like [out1]=functionName(in1,in2)

As my program is complex I d like to reduce the memory requirement and have fast execution.

Answers

Depending on the structure of your algorithm, there s likely to be a third option, which is to use nested functions. A nested function has its own workspace (variable scope), but also has access to variables in the workspaces of functions within which it is nested - without them being properly global.

Whenever I ve implemented recursive functions in MATLAB I ve found this to be an approach which typically makes the code quite clean.

Here s a simple arithmetic example:

function z = times1(x,y)

if y == 0
    z = 0;
else
    z = plusy(times1(x, y-1));
end

    function z = plusy(x)
    z = x+y;
    end

end

You can see that the variable y is used within the nested function plusy even though it s not an input argument, but in the workspace of the parent function; nevertheless it s not a global. (Note that in recent versions of MATLAB, y will be coloured light blue in the editor to emphasize this shared scope).

http://www.mathworks.com/matlabcentral/fileexchange/18798 http://www.mathworks.com/matlabcentral/fileexchange/18798

Source

License : cc by-sa 3.0

http://stackoverflow.com/questions/8148982/global-variables-and-arguments-in-matlab-which-is-fastest

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