undefined input argument using nlinfit

Hi! i am using an nlinfit to determine a model parameter but i kept getting this error:

Input argument "data" is undefined.

even though i already defined the argument data. For clarity i will post the syntax here:

%input data;

%data [T(K) B(m3/gmol)];
data=[330 -9.7707
370 -7.3893
410 -5.6488
450 -4.3256
490 -3.2880
530 -2.4538
570 -1.7695
610 -1.1984
650 -0.71487
690 -0.30045
730 0.058557];

Gc=83.1451e-6;

Bact=data(:,2)
Tact=data(:,1)

unk0=[374 0.1 16]; %[Tc w Pc] in order, initial guess;

[unkhat resid J]=nlinfit(data,Bact,pct,unk0);

unkhat

the function pct is defined on a separate m-file.

is there anything i missed that i kept geting that error? i will gladly appreciate your help. thank you.

Answer 1

[the cyclist]

Marineil,

I am confused a bit by your code. Because you did not include your definition of "pct", I created a simple one. When I do that, I do not get any error about the input parameter "data". I do get a warning about the resulting Jacobian, but I think that is because one of your X columns is defined as exactly the same as your Y column, in the call to nlinfit(). [I am wondering if you meant to just input "Tact" as the first argument to nlinfit(), rather than the whole array "data".]

Maybe you could also post your function definition for "pct", so that we can see exactly what you are running?

[Marineil Gomez]

i apologize for not providing the m-file. this is the pct function

function [ Bcal ] = pct(unk,data)

%PCT Summary of this function goes here

% Detailed explanation goes here

Gc=83.1451e-6;

Tact=data(:,1);

F0=0.1445-(0.330./(Tact./unk(1)))-(0.1385./(Tact./unk(1)).^2)-(0.0121./(Tact./unk(1))^3)-(0.000607./(Tact./unk(1)).^8);

F1=0.0637+(0.331./(Tact./unk(1)).^2)-(0.423./(Tact./unk(1)).^3)-(0.008./(Tact./unk(1)).^8);

Bfunct=F0+unk(2).*F1;

Bcal=(Gc*unk(1).*Bfunct)./unk(3);

thanks for your help!