Re: Delayed Evaluation of NDSolve Arguments

*To*: mathgroup at smc.vnet.net*Subject*: [mg62973] Re: Delayed Evaluation of NDSolve Arguments*From*: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>*Date*: Fri, 9 Dec 2005 06:19:42 -0500 (EST)*Organization*: Uni Leipzig*References*: <dnbmas$5ks$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, f[t_?NumericQ] := 1; sol = NDSolve[{x'[t] == f[t], x[0] == 0}, x[t], {t, 0, 1}]; Plot[Evaluate[x[t] /. sol[[1]]], {t, 0, 1}] Regards Jens "ben" <benjamin.friedrich at gmail.com> schrieb im Newsbeitrag news:dnbmas$5ks$1 at smc.vnet.net... | Dear All, | | is there a way to prevent NDSolve to evaluate its arguments | right on the spot? | | Inside my differential equation | | x'[t]=F[x[t],t,f[x[t],t]], | | I want to use a function f[x,t] which | makes only sense, when called with | numeric arguments. | So everything would be fine, if NDSolve | would evaluate the differential equation | at each time step. | However, the differential equation is only | evaluated once at the beginning, and | then only numerical values are plugged | into the evaluated equation at each time step. | | Below is a baby example of my problem | | f[t_]:=If[NumericQ[t],1,0]; | | sol=NDSolve[{x'[t]==f[t],x[0]==0},x[t],{t,0,1}]; | | x[t]/.sol[[1]] | 0. | (* I want x[t]=t ! *) | | Any help would be appreciated | Benjamin |