Guessing the values of a function by using initial values

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Ahmet Emre 2022-8-3

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编辑： Torsten 2022-8-5

Hey there,

I have been trying to use Newton Raphson method in order to get Matlab to guess some unknowns of a function. Hovewer, I did not have any luck doing that. Is there a better way to guess the values of a function?

Also the function I am working on is "f(x,y)=x-((28+y)/2)". And the initial values are; x_init=26.94 y_init=25.87.

Is it a right approach to use Newton Raphson method, or is there a way in Matlab to guess the variables of a function?

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Torsten 2022-8-4

编辑：Torsten 2022-8-5

In parameter estimation, you usually have more equations than unknown. The usual Newton-Raphson does not apply in this case.

Look up "Gauss-Newton-algorithm" for more details:

https://en.wikipedia.org/wiki/Gauss%E2%80%93Newton_algorithm

In MATLAB, the functions "lsqlin" (for linear problems) or "lsqcurvefit" (for nonlinear problems) should do what you want.

Ahmet Emre 2022-8-5

Thank you for the answer, I'll check that function

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回答（1 个）

Les Beckham 2022-8-3

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编辑：Les Beckham 2022-8-3

在 MATLAB Online 中打开

You don't have to "guess" the values of the function, you can just calculate them.

Example

x = [-20:.1:20];

y = x;

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

f = @(x,y) x-((28+y)/2)

f = function_handle with value:

@(x,y)x-((28+y)/2)

Z = f(X,Y);

h = surf(X,Y,Z);

h.EdgeColor = 'none';

If you are trying to find the zeros of the function, that is a different question.

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Ahmet Emre 2022-8-3

I also need to run this in an iteration to get every calculated value of x and y and assign those to separate arrays. Say, to create an 1x64 array. That way, I will be able to solve my problem. I guess the solution you provided only gives certain points. This is the reason I was curious if it would somehow be possible to create "guess values". Thank you, by the way.