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

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Ibraheem
Ibraheem 2022-10-13
编辑： James Tursa 2022-10-13
I trying to use fmin search for a function of 2 variable

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James Tursa
James Tursa 2022-10-13
编辑：James Tursa 2022-10-13
Ran in:
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
James Tursa 2022-10-13
编辑：James Tursa 2022-10-13
Ran in:
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

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the cyclist
the cyclist 2022-10-13
编辑：the cyclist 2022-10-13
Ran in:
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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