lsqcurvefit - Error using Data_fit>@​(x)myfun2(​x,xdata) Too many input arguments.

Hello,

I am having this error in the title running a lsqcurvefit program. I'm not very proficient in MATLAB and I think I'm making some simple mistakes which I just could not figure out. I checked similar questions asked before and consulted documentation but still culd not figure out. Hence this plea for help.

I am trying to do a least sq fit for an implicit function, i.,e, I need to solve an equation with a given set of optimizing parameters x to get the function that is being optimized. I'm doing a fit also with another function that is explicit and that is working fine.

Here is the code.

I would appreciate help anyone can provide.

Thank you.

Sid

P.S. There are some leftover codes left from trying various things like N not being passed in the E_fun and putting a dimension statement for y in the E_fun, etc.

------------

div1=5.4/6.4;
N=11;
B_max=10.0;
xdata=zeros(1,N);
x_D=zeros(1,N);
g=zeros(1,N);
beta=zeros(1,N);
x=zeros(1,2);

ydata = [6.4, 6.5, 6.8, 7.1, 7.5, 8.0, 9.0, 10.0, 11.0, 11.7, 12.5]; %in units of inch divs

for i=1:11
    B=(i-1)*1.0;
    xdata(i)=B;
    ydata(i)=div1*ydata(i);
end
fun_DF = @(x,xdata)x(1).*(1+0.25.*((1.73.*xdata./x(1)).^2)).^0.5;
x0=(5.4);
lb=4.0;
ub=6.0;
[x,resnorm,residual,exitflag,output] = lsqcurvefit(fun_DF,x0,xdata,ydata,lb,ub);
fprintf('\nFD eps0= %.3f\t resnorm= %.3f\n',x, resnorm);

times = linspace(xdata(1),xdata(end));
plot(xdata,ydata,'ko',times,fun_DF(x,times),'b-')

%Parabolic potentail
x0=[5.0, 0.1];
lb=[4.0, 0.01];
ub=[6.0, 1.0];
myfun2 = @(x,xdata) E_fn(x,xdata);  % parameterized function
fun2 = @(x) myfun2(x,xdata);    % function of x alone; x(1)=eps0, x(2)=alpha0
[x,resnorm,residual,exitflag,output] = lsqcurvefit(fun2,x0,xdata,ydata,lb,ub);
fprintf('\nexp eps0= %.3f alpha0= %.3f\t resnorm= %.3f',x, resnorm);

function output = E_fn(x,xdata)
    N=11;
    y=zeros(1,N);
    eps0=x(1);
    alpha0=x(2);
    beta=11.75*alpha0*alpha0/eps0;
    for i=1:N
        g=(1.0+0.25*(1.73*xdata(i)/eps0)^2)^0.5;
        myfun3 = @(xd, beta, g) x_D_fn(xd, beta, g);  % parameterized function
        fun3 = @(xd) myfun3(xd, beta, g);    % function of x alone
        [theroot, fval, exitflag, output] = fzero(fun3, 0.7);
        x_D = theroot;
        f=(1.0+(g*g-1)/(g*x_D*x_D)^2)*g*x_D*x_D+(0.5/beta)*(1-1/(1+2*beta/(g*x_D*x_D)));
        y(i)=0.5*eps0*f;
    end
    output=y;
end

function y=x_D_fn(x,beta,g)
    y=x^4-1/(g*(1+2*beta/(g*x*x)))^2-(g*g-1)/(g*g);
end

Answer 1

[Matt J]

The second call to lsqcurvefit should be,

___ = lsqcurvefit(@E_fn,x0,xdata,ydata,lb,ub);

or

___ = lsqcurvefit(myfun2,x0,xdata,ydata,lb,ub);

[Sid Chaudhuri]

Matt,

Wow! Awesome! I used @E_fun and it worked. Clearly I don't understand the logic of the paramterized function statement. I wasted many hours to fix this what you told me right away. Now I'm having difficulty in the following plot statement and I tried E_fu, @E_fun, Myfun2 and I am getting error "Vectors must be the same length." What am I doing wrong?

Thank you so much for your help.

Sid

Note: I changed teh variable x for teh second function to xe so I can use in the plot and rewrite it for teh first function.

times = linspace(xdata(1),xdata(end));

plot(xdata,ydata,'ko',times,fun_DF(x,times),'--',times,E_fn(xe,times),'b-')

[Matt J]

Like the error message says ... one of your x,y data pairs can't be plotted because they are not the same length.

[Sid Chaudhuri]

Yup. Now I see that my E_fun is hardcoded at N=11 because I couldn't pass the N parameter. I tried to cange the E_fun def line to "myfun2 = @(xe,xdata,N) E_fn(xe,xdata,N); and correspondingly to the function E_fun. That did not work. How could I pass N to E_fun function?

Thanks a lot.