MATLAB: Optimization: share additional output of cost function with constraint function

costfminconMATLABoptimization

I have a well defined optimization problem in which I have a separate cost function and a separate constraint function:
Cost = @(C)costcenterroad(C,lp,xref,yref,T,rw);
Nonlinconstr=@(C)nonlcon(C,lp,rw,xref,yref,sol);
[C,fval] = fmincon(Cost,C1,[],[],[],[],[],[],Nonlinconstr);
Inside the cost function (which is called first by fmincon), I evaluate nonlinear functions of the decision variables (C in this case). The outputs of the nonlinear function determine the cost.
However, in the constraint function I need to evaluate the same function, with the same decesion variables (thats the way fmincon works; first the cost, then the contraints). Hence, I would rather use the values already calculated in the cost functions.
I tried to do this by using a structure SOL as an output of the cost function, and provide it as an input to the constraint function hence (also see code above);
function [J,sol]=costcenterroad(C,lp,xref,yref,T,rw)
function [c,ceq]=nonlcon(C,lp,rw,xref,yref,sol)
However, Matlab will tell that "sol" is unknown. I'am guessing that "sol" is not an output when the function `costcenterroad` is called. I also used 'sol' as a global variable, but this is not very elegant and fast.
Does anyone have any suggestions how to do this? Your help will be greatly appreciated!

Best Answer

There was a good discussion on this issue here: http://www.mathworks.com/matlabcentral/newsreader/view_thread/269936
The technical term for this practice is "Memoization". There's some more good information on memoization in MATLAB in Loren's blog post:
http://blogs.mathworks.com/loren/2006/02/08/use-nested-functions-to-memoize-costly-functions/
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