Re: constrained FindFit is extremely slow?

*To*: mathgroup at smc.vnet.net*Subject*: [mg131758] Re: constrained FindFit is extremely slow?*From*: Joe Gwinn <joegwinn at comcast.net>*Date*: Sat, 28 Sep 2013 21:25:08 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net*References*: <l143o7$pqn$1@smc.vnet.net>

In article <l143o7$pqn$1 at smc.vnet.net>, dantimatter <google at dantimatter.com> wrote: > hi all > i'm trying to use FindFit to find parameters in a differential equation > model, and give it a bit of help by adding constraints. But i'm finding that > as soon as i add a single constraint, Mathematica grinds to a halt. is this > something specifically to do with the differential equation model? Yes, it changes algorithm. I use EvaluationMonitor to follow the moves the solver is making. This is from the online documentation of FindFit: Block[{count=0},{FindFit[data,60+70 Exp[-a x],a,x,EvaluationMonitor:>count++],count}] If you see it bouncing along a line, the solver is doing linear-programming tricks, walking along the intersection of two constraint hyperplanes. Figuring this all out can be pretty fiddly. Good Luck Joe Gwinn > code is: > > > model[a_?NumberQ,b_?NumberQ,c_?NumberQ,d_?NumberQ,f_?NumberQ,Km1_?NumberQ,Km2_? > NumberQ,Km3_?NumberQ,NTP0_?NumberQ]:=(model[a,b,c,d, f, > Km1,Km2,Km3,NTP0]=First[MG/.NDSolve[{ > MG'[t]==a*DNA*NTP[t]/(Sqrt[Km1^2]+NTP[t])-b MG[t], > NTP'[t]==-f*a*DNA*NTP[t]/(Sqrt[Km1^2]+NTP[t])-d MG[t] > NTP[t]/(Sqrt[Km2^2]+NTP[t])-c NTP[t]/(Sqrt[Km3^2]+NTP[t]), > NTP[0]==NTP0,MG[0]==0},{MG,NTP},{t,0,800},Method->StiffnessSwitching]]); > > fit = FindFit[data, > model[a, b, c, d, f, Km1, Km2, Km3, NTP0][ > t], {{a, 10}, {b, 0.0737}, {c, 7}, {d, .99}, {f, 18}, {Km1, > 12893.842}, {Km2, 8663.477}, {Km3, 1946}, {NTP0, 1500000}}, t] > > thanks! >