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aroberts1-Visitor
1-Visitor
January 21, 2012
Solved

Help Needed Curve-Fitting 3rd Order Transfer Function

  • January 21, 2012
  • 4 replies
  • 5466 views

I have collected data points for a system that can be modeled by a third order transfer function (G= 1/(ax^3+ bx^2+cx^1+d)), at resonance. I would like to try and curve fit the data so I can analyze the experimental with the model but I cant figure out how to do it. I have tried the pwrfit and genfit commands but without luck. The plot of experimental data is included.

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Best answer by ViktorKorobov

Anthony,

See in attach

4 replies

V
VladimirN24-Ruby III
24-Ruby III
January 21, 2012

Please attach to the message (by using "Use advanced editor") your Mathcad worksheet.

R
RichardJ19-Tanzanite
19-Tanzanite
January 21, 2012

This is easy to do. Genfit is one approach, but minerr is a better one. Please post a worksheet with the data and the equation for the model and I (or someone else if they beat me to it) will show you how to do it.

A
aroberts1-VisitorAuthor
1-Visitor
January 22, 2012

I have attached the data set and form of the equation.

V
ViktorKorobov1-VisitorAnswer
1-Visitor
January 22, 2012

Anthony,

See in attach

A
aroberts1-VisitorAuthor
1-Visitor
January 23, 2012

Thank you, this helps immensely. How did you come up with your initial guesses though (vg)?

V
ValeryOchkov24-Ruby IV
24-Ruby IV
January 22, 2012

Try please Mathcad server with this task (genfit):

http://twtmas.mpei.ac.ru/mas/worksheets/Fit_f_x_a_b_c.mcd

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