Memoizing Functions in MatLab

Three less known features of MatLab allow for memoizing functions:

• nested functions
• property lists on Variables
• function handles

Code:

function mf = memoize(f)
    % Returns the memoized version of function f.
    % f must have exactly one numerical argument.
    % The memoized version cannot be called without an argument.
    % Memoizing functions of continous ranges 
    % may not be as useful as imagined...
    
    h = []; % our pseudo hashtable by abuse of the property list.
            % MatLab creates this fresh for every call of memoize
            % and retains it for the lifetime of the memoized function

    function r = ff(x)

            % matlab allows only "MatLab words" as keys
            xstr= ['m', num2str(x)];
            if isfield(h, xstr)
                   r=h.(xstr);
            else
                   h.(xstr) = f(x);
                   r = h.(xstr);
            end
    end

    mf = @ff;
end

Test with e.g.

function o = foo(x)
	pause on
	pause 5
	o = x*x
end

Call

mfoo = memoize(@foo); 
foo(4)
foo(4)
mfoo(4)
mfoo(4)

Mon, 11 Mar 2013
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