my fminsearch function doesn't get the optimum values

Question

Jeremy Choo 2021-10-16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1565186-my-fminsearch-function-doesn-t-get-the-optimum-values

评论： Star Strider 2021-10-16

I've tried to do a very simple problem by finding out the optimal x and y with x0 = 1, y0 = 1 for the function f (x, y) = 2xy +5x − 2x^2 −3y^2 +10.

I have no idea what I'm doing so I assumed x = x(1) and y = x(2) and did the function as follows:

function y = tut2(x)

y = 2*x(1)*x(2)+5*x(1)-2*x(1)^2-3*x(2)^2+10;

I then called the thing in the command window:

>> [x,fval] = fminsearch(@tut2,[1,1]), which should have given me x and y values of 3/2 and 1/2 respectively, which are the correct answers to the solution. However, they don't. May I know what went wrong in my coding? The fminsearch website told me to use x(1) and x(2) as the initial points, so why is the function not working?

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Answer 1

Star Strider 2021-10-16

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1565186-my-fminsearch-function-doesn-t-get-the-optimum-values#answer_809971

在 MATLAB Online 中打开

The fminsearch function searches for a minimum. To get a maximum, negate the function —

[x,fval] = fminsearch(@(x)-tut2(x),[1,1])
x = 1×2
    1.5000    0.5000
fval = -13.7500
function y = tut2(x)
y = 2*x(1)*x(2)+5*x(1)-2*x(1)^2-3*x(2)^2+10;
end