find the solutions of h(x)=(x^8+P(x))^2 which give local minimum (fminsearch).....any help?

i dont know what function i have to write and also when i write xmin=fminsearch(.....) what i must write inside the space??

[jgg]

What is P(x) in your example? The easiest way to do this is to call an anonymous function:

 x0 = 0; %for example
 h = @(x)((x^8 + P(x))^2);
 x = fminsearch(h,x0);

But this depends on what P(x) is here. If fminsearch is not required, you might consider something like lsqnonlin instead.

[andreas tziolas]

ok thank you..doing it by this way i dont have to create a function?

Answer 1

[Star Strider]

If P(x) is a 7-degree polynomial derived from polyfit:

p = randi(9, 1, 7);                                 % Create Data (Polynomial Coefficients)

f = @(x,p) x.^8 + polyval(p,x).^2;                  % Function
x0 = 2;                                             % Initial Estimate For ‘x’
[xmin,fval] = fminsearch(@(x)f(x,p), x0);           % Find Minimum

You have likely gotten ‘p’ from something other than randi, but I had to create something to test the code.

[andreas tziolas]

it shows me an error Error in fminsearch (line 190) fv(:,1) = funfcn(x,varargin{:});

[Star Strider]

It ran for me (in R2015b) without error, or I’d not have posted it.

I don’t understand that error. There must be more to it.