Delayed Evaluation of NDSolve Arguments

*To*: mathgroup at smc.vnet.net*Subject*: [mg62945] Delayed Evaluation of NDSolve Arguments*From*: "ben" <benjamin.friedrich at gmail.com>*Date*: Fri, 9 Dec 2005 05:10:26 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

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