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