MATLAB: Find specific point in unknown “function”

algorithmoptimization

Hello,

I have the following problem:

I do know the "shape" of the relationship between two variables x and y, but I don't know the exact values and it takes a lot of time to calculate them.. (for each x I can find an y)

I'm interested in finding the point, where y=1. To get there I want to have to calculate as few values as possible.

Does anyone know an algorithm, that could help me do this and is more "efficient" than just increeasing gradualy x from x_start till I get the desired y?

Thanks in advance!

PS: here you can see the genmeral shape of the relationship:

Best Answer

The most efficient way is to use fzero as Torsten said. Your function is @(x)y(x)-1. For the most efficiency, set the initial point x0 to an interval [x1,x2] where the function changes sign between x1 and x2.

Alan Weiss

MATLAB mathematical toolbox documentation

P.S. If you have Optimization Toolbox, then fsolve can be even faster than fzero.

Related Solutions

MATLAB: Find optimized x1, x2, x3 for a given y.

y = 2;
fun = @(x) (x(1).^2 + 2.*x(1).*x(2) + x(3).^2 - y).^2
bestx = ga(fun, 3);
x1 = bestx(1); x2 = bestx(2); x3 = bestx(3);

Note: there are an infinite number of solutions. It does not start to get interesting until you put on constraints.

MATLAB: How to “solve” a “function”

The issue here is that you cannot reverse engineer this kind of function. If you know the average and lets say you know the size of the vector that gave the average, still can not determine the vector by any method or algorithm using any program in the world.

you can understand it like this: Lets say the average is 10 and size of vector is 2. then possible solutions will be [0 20],[9 11], [10 10] and many many many more. You can never figure out (unless you have some other information) which was the original vector that gave you the average of 10.

Best Answer

Related Solutions

MATLAB: Find optimized x1, x2, x3 for a given y.

MATLAB: How to “solve” a “function”

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