writing objective function for error optimization

I'm trying to write an objective function like:

function y = parameterfun(xin,sig)
a=trapz(sig);
b=sig;
y= xin(1)*b+xin(2)*a;
xin0=[1,1];
f = @(x)parameterfun(x,sig);
[xin,fval] = fminunc(f,xin0);

sig is a double data type,actually it is an error signal that I want to find out for which parameters xin(1),xin(2) would be minimum. I do not know why i'm getting this:

Error using parameterfun (line 2)
Not enough input arguments.

can anybody help me with that?I would really appreciate.

[Matt J]

You seem to have mushed together the objective function with the optimization code that invokes it. Are these lines really part of the objective function, too?

xin0=[1,1];
f = @(x)parameterfun(x,sig);
[xin,fval] = fminunc(f,xin0);

[Navid]

firstly thanks for your respond,actually I've updated the code with help of @Mischa , but it has still error,can you see that please?

Answer 1

[Mischa Kim]

Navid, I believe, that's what you would like to do:

 function test()                           % setting up optim. problem
 x0   = [1,1];
 sig0 = 1;
 xin0 = [x0 sig0];                         % initial solution guess
 [xin,fval] = fminunc(@parameterfun,xin0); % execute optimization
 end

 function y = parameterfun(xin)
 xin1 = xin(1);
 xin2 = xin(2);
 sig  = xin(3);

 a = trapz(sig);
 b = sig;
 y = xin1*b + xin2*a;
 end

Put the two functions in one function file (e.g., called test.m) and don't forget to assign a value to sig. The way you have set it up you are using parameterfun() recursively. Was this intended?

[Navid]

Many thanks for your help,the point is that I have to use the sig as an input argument,because as I mentioned it is a double data type which I'm using itself and also it's integral in order to compute my system's error.

[Mischa Kim]

You could just call the function with sig0 as an input argument

 function test(sig0)

What exactly is sig? Can you paste in a comment?

[Navid]

I did some changes to the code:

function test()                                                            
 x0   = [1,1];
 sig = evalin('base','sig');  %importing vector sig from workspace                                             
 xin0 = [x0];                                                              
 [xin,fval] = fmincon(@parameterfun,xin0,[],[],[],[],[1,1],[100,100]);     
 end
 function y = parameterfun(xin)
 sig = evalin('base','sig');
 xin1 = xin(1);
 xin2 = xin(2);
 a = trapz(sig);
 b = sig;
 y = xin1*b + xin2*a;
 end

and now I'm getting this error:

Error using fmincon (line 708)
User supplied objective function must return a scalar value.

Error in test (line 5)
 xin = fmincon(@parameterfun,xin0,[],[],[],[],[1,1],[100,100]);     %
 execute optimization

I've also attached the vector sig to make it more clear. I would appreciate any help.