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MathGroup Archive 2008

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How to find the best fit for a list {x,y} of data

  • To: mathgroup at smc.vnet.net
  • Subject: [mg91888] How to find the best fit for a list {x,y} of data
  • From: dinodeblasio at gmail.com
  • Date: Fri, 12 Sep 2008 05:25:14 -0400 (EDT)

Hello everybody,
I have the list and the y=f(x) equation

data = {{1, 1}, {28, 0.719188377}, {54, 0.35746493}, {81,
    0.182114228}, {117, 0.166082164}, {260, 0.132765531}};
express = (1 - k*x)*(1 - k*x/q)*(1 - p*k*x/q)

(1 - k x) (1 - (k x)/q) (1 - (k p x)/q)


"k,q and p are parameters; then I do the fitting":

f1 = FindFit[data, (1 - k*x)*(1 - k*x/q)*(1 - p*k*x/q), {{k, 0.01},
{p, 1.5}, {q,1}}, x, MaxIterations -> 200]

"and I obtain":

{k -> 0.00586032, p -> 2.86841, q -> 2.86841}

"My question is: how I can find the best fit to my data for values of
(k,q,p) >0" ??

Thank you very much for your help.
Dino


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