Re: Efficient repeated use of FindRoot

*To*: mathgroup at smc.vnet.net*Subject*: [mg74060] Re: [mg74049] Efficient repeated use of FindRoot*From*: "Chris Chiasson" <chris at chiasson.name>*Date*: Thu, 8 Mar 2007 04:35:00 -0500 (EST)*References*: <200703070816.DAA26723@smc.vnet.net>

Why are you not using NMinimize or NMaximize? On 3/7/07, Michael A. Gilchrist <mikeg at utk.edu> wrote: > Hi all, > > I've got an optimization problem that I am trying to evaluate numerically > and at a number of different points of a particular variable. I am using > a Lagrangian multiplier to impose a constraint on the optimization of the > 'free variables' and as a result trying to find the root for a set of n > coupled equations (in its full form n = 4000+ variables). > > > Using some approximations I can come up with some reasonable initial > conditions, but, as you might imagine, it takes quite some time to run > the code. Looking at the output it appears that the greatest amount of > time is initialization of the FindRoot routine (once the routine is > running it calculates each step quite quickly). > > > Here's some pseudo code to illustrate the basic idea: > > (*set up eqns and variables*) > Clear[m]; > vars = Table[m[i], {1, n}] > > eqns = Table[ > (llik[i, vars] + \[Lambda] m[i] ==0), {i, 2, n}] > (*llik previously defined) > ics = Table[ > m0[i] = T[i]/phi[i] (*T[i] and Phi[i] previously defined*), > {i, 2, n}]; > > frvars = Table[{m[i], m0[i] * 0.01, m0[i]*10}, {i, 2, n}]; > > > (*look for solution to problem for multiple values of m[1] *) > Table[ > FindRoot[eqns, frvars], {m[1], 0.01, 0.2, 0.01}] > > > I am aware of the NDSolve package StateData that allows one to > efficiently evaluate DE's with various different initial > conditions by processing the equations. > > I've looked through the documentation on FindRoot and haven't found a > similar routine/ability. I'm wondering if anyone has any ideas on how > one might increase the efficiency of my calculations. > > Thanks. > > Mike > > > ----------------------------------------------------- > Department of Ecology & Evolutionary Biology > 569 Dabney Hall > University of Tennessee > Knoxville, TN 37996-1610 > > phone:(865) 974-6453 > fax: (865) 974-6042 > > web: http://eeb.bio.utk.edu/gilchrist.asp > ----------------------------------------------------- > > > -- http://chris.chiasson.name/

**References**:**Efficient repeated use of FindRoot***From:*"Michael A. Gilchrist" <mikeg@utk.edu>