Want to create a 3d graph of chi^2 for a 2d data set /w 3 parameters

Asked by Jake on 26 Jun 2012

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Hi, Ive recently been modifying a short simulated annealing algorithm that fits decay curves. I'm currently trying to minimize a weighted r sqrd function and I would like to see what a surface mesh graph of the solution space is. I have 2 parameters (Ae^kt) and two data sets (Time, signal (1001 data points) and I keep on running into a 'matrix has to been same size to use .*' The code im trying to use is:

[X,Y] = meshgrid(80:1:120, -.1:.005:0); Z = (1/1001)*sum((X.*exp(Y.*Time)-signal).^2)./sqrt(signal); surf(X,Y,Z)

Where X,Y are A,k. Z should be single valued, how can i formulate this so matlab treats A,k as free variables and plots Z in the 3rd dimension?

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Answer by Stephen on 26 Jun 2012

it looks like X and Y are not a single value, but the result of meshgrid, and when you perform the .* operations with the 1001 element vectors you see and error because the dimensions mismatch. Try using 1 time and signal point, or make a meshgrid with signal and time and use 1 A,k pair.

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