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 User defined function for fitting of data!!		  New Topic  Reply to Topic
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coffeezombie

Korea
1 Posts
Posted - 10/12/2011 :  09:29:28 AM  Show Profile  Edit Topic  Reply with Quote  View user's IP address  Delete Topic
Origin Ver.: 8.0
Operating System: Windows XP

HI!! GUYS!!
I'd like to fit power like data with not built-in power function (y = (a*(1-x^b))^c )

Hence, I made user-defined function of y = [/b](a*(1-x^b))^c[/b]
If function is y = a*(1-x^b), It is simple. The problem is that I cannot find suitable code about variable c.
The detail of y =a*(1-x^b) is as follows.

sort(x_y_curve);
x_y_curve = ln(x_y_curve);
Dataset dx;
x_y_curve.AttachX(dx);
dx=ln(1-dx);
double coeff[2];
fitpoly(x_y_curve,1,coeff);
a=exp(coeff[0]);
b=coeff[1];


What should I do for it?
With best regards,

Sam Fang

293 Posts
Posted - 10/19/2011 :  05:52:00 AM  Show Profile  Edit Reply  Reply with Quote  View user's IP address  Delete Reply
From your script, it seems that your function is:

y=a*(1-x)^b


You should confirm that your power function is

y=(a*(1-x^b))^c


or


y=(a*(1-x)^b)^c


For the latter, over-parameterization exists, there is no unique solution and you should apply constraints.

Sam
OriginLab Technical Services
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