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Hello all, thanks for looking.

For example if I have composite material consisting of concentrations of A and B and their resulting measured stress value is Z (in picture below this is the matrix in green). Now given the value of z, how do I find the value of A and B which correspond to it?

Usually the interp2 would work if I know A and B and want to find Z value, but now I want to do the opposite. The z value is beyond the range of results too, so may need to be extrapolated.

I currently have the script below whcih plots a surface sketch but I want to essentially find x and y values that correspond to a specific z value. I assigned the A concentration as x, B concentration as y and the stress value of thir combination z.

So as an exmaple, I want to know x and y values that would make z=0.4.

Many thanks for your help!

x=[2.5; 5]

y=[1; 1.5]

z=[4.9 5.3; 13.8 14.4]

surf(x,y,z)

Ameer Hamza
on 22 May 2020

Edited: Ameer Hamza
on 22 May 2020

As mentioned in the comment to your other question, if you try to extrapolate the surface that there is not a unique solution corresponding to a given z value. The following shows one of the ways; however, you can note that the solution is different every time you run it. It is because each initial guess to fsolve() will lead to a different solution.

x=[2.5; 5];

y=[1; 1.5];

z=[4.9 5.3; 13.8 14.4];

[X,Y] = meshgrid(x,y);

mdl = scatteredInterpolant(X(:), Y(:), z(:));

fun = @(x) mdl(x(1),x(2));

sol = fsolve(@(x) fun(x)-0.4, rand(1,2));

x_sol = sol(1);

y_sol = sol(2);

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## Direct link to this comment

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