my fminsearch function doesn't get the optimum values

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?

Answer 1

[Star Strider]

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

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[Jeremy Choo]

Thank you so much!

[Star Strider]

As always, my pleasure!

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