MATLAB: How to converge curve with fminsearch with the code given below

i find all the values of y2 as infinity

I am doing curve fitting using fminsearch . My code is like…
X=....
Y=....
X1=(X./(42*(10^-9)));
 Y1=(Y./(pi*((5*10^-6)*(5*10^-6))));
 Q=sqrt(X1);
 P=(Y1./X1);
  plot(Q,log(P)./log(exp(1)),'o');
    hold on
    A= 5.53*(10^(-17));
    B= 2.6*(10^(-19));
    C= 4.26*(10^(48));
     x0=fminsearch('function_2',[A B C]);
  %  

   A=x0(1)                                                                                                           
   B=x0(2)
   C=x0(3)
   x2=linspace(min(Q),max(Q),100);
    x3=linspace(min(X1),max(X1),100);
    xp=x3.';
    y2=(C.*(exp((B.*sqrt(x3))-A)));
    yp=y2.'
   V=(y2./x3)
plot(x2,log(V)./log(exp(1)),'m.')
%legend('meas','fitted')

 grid on
Dont know why I am having all infinite in my 'y2 '?
Any suggestion is appreciable.
…..Ayesha
   x0=fminsearch('function_2',[A B C]);
%  
 A=x0(1)                                                                                                           
 B=x0(2)
 C=x0(3)
 x2=linspace(min(Q),max(Q),100);
  x3=linspace(min(X1),max(X1),100);
  xp=x3.';
  y2=(C.*(exp((B.*sqrt(x3))-A)));
  yp=y2.'
  V=(y2./x3)
plot(x2,log(V)./log(exp(1)),'m.')
%legend('meas','fitted')
 grid on

Best Answer

I do not see ‘function_2’ anywhere, so I have no idea what it is doing. The function you minimise has to take one argument (the parameter vector you want to minimise) and return one scalar value.
Since ‘function_2’ appears to be external to your code (and not an anonymous function, for example), call it instead as:
x0=fminsearch(@function_2, [A B C]);
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