Re: Why doesn't this work?

*To*: mathgroup at smc.vnet.net*Subject*: [mg20389] Re: Why doesn't this work?*From*: steve at smc.vnet.net*Date*: Mon, 18 Oct 1999 02:40:33 -0400*References*: <7u9098$qg5@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com*Wfrom*: phbrf@t-online.de (Peter Breitfeld)

Joe Strout <joe at strout.net> schrieb: > I'm trying to understand why a temporary is needed in the following > case. I've got a function of one parameter and two constants. I > define the constants on the fly with "/.". I want to find a root of > this equation. When I use "/." in FindRoot, it doesn't work, but if I > create another function that has these as true constants (rather than > symbols), FindRoot works. I don't understand why these two cases are > different. > > Here's my function (a difference of gaussians): > > Dog[t_] := (t/tau1)^6 * Exp[-6 * (t/tau1 - 1)] - (t/tau2)^6 * Exp[-6 * > (t/tau2 - 1)] > > Here's my first attempt to find a root, and the result: > > FindRoot[(Dog[t]==0) /. { tau1->13.7, tau2->24.8}, {t, 20}] > FindRoot::frnum: Function {False} is not a length 1 list of numbers at > {t} = {20.}. [*** snipp ***] Joe, FindRoot[Evaluate[(Dog[t]==0) /. { tau1->13.7, tau2->24.8}], {t, 20}] works. Peter =--=--=--=--=--=--=--=--=--=--=--=--= http://home.t-online.de/home/phbrf =--= =--= Peter Breitfeld, Saulgau, Germany PGP public key: 08548045 =--=--=