How do i use fminsearch to find the minimum or maximum of a function . x.^4-3.x.y+2.*y.^2

You need to have your function handle accept a vector and return a scalar. I.e., the x argument to the function handle is a vector of two elements representing your original x and y variables. Assuming x(1) and x(2) are your intended original x and y variables, that would mean something like this:

fun = @(x) x(1).^4-3.*x(1).*x(2) +2.*x(2).^2;
x0 = [-0.5,0.5];
x = fminsearch(fun,x0)
x = 1×2
   -0.7500   -0.5625

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James Tursa 2022-10-13

编辑：James Tursa 2022-10-13

在 MATLAB Online 中打开

format longg
fun = @(x) x(1).^4-3.*x(1).*x(2) +2.*x(2).^2;
x0 = [-0.5,0.5];
x = fminsearch(fun,x0)
x = 1×2
        -0.749979058202537        -0.562478134566371
fun(x)
ans = 
        -0.316406248937402
fun([3/4,9/16])
ans = 
               -0.31640625

Also note that fminsearch( ) can only find local minimums, of which there can be more than one depending on the function. So different starting points can result in different answers.

x = fminsearch(fun,[3/4+0.1,9/16-0.1])
x = 1×2
         0.749992146496559         0.562470511151394
fun(x)
ans = 
        -0.316406248747428

the cyclist 2022-10-13

The function is invariant in the transformation (x,y) --> (-x,-y)

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Answer 2

the cyclist 2022-10-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1824248-how-do-i-use-fminsearch-to-find-the-minimum-or-maximum-of-a-function-x-4-3-x-y-2-y-2#answer_1073053

编辑：the cyclist 2022-10-13

在 MATLAB Online 中打开

Did you try reading the documentation for fminsearch? The very first example is exactly like your problem.

fun = @(x)(x(1)^4 - 3*x(1)*x(2) + 2*x(2)^2);
x0 = [-0.5, 0.5];
x = fminsearch(fun,x0)
x = 1×2
   -0.7500   -0.5625

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