Re: Re: NDSolve Question

*To*: mathgroup at smc.vnet.net*Subject*: [mg86385] Re: [mg86357] Re: NDSolve Question*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Mon, 10 Mar 2008 02:02:41 -0500 (EST)*Reply-to*: hanlonr at cox.net

f[q_?NumericQ] := q; This function is not very useful as an example since DSolve[{x'[t] == x[t], x[0] == 0}, x[t], t][[1]] {x[t] -> 0} With a slight change DSolve[{x'[t] == x[t] + 2, x[0] == 0}, x[t], t][[1]] {x[t] -> 2*(-1 + E^t)} f[q_?NumericQ] := q + 2; Note that NumericQ is better than NumberQ so that f will evaluate with arguments like Pi or E f[3 Pi] 2 + 3*Pi sol = NDSolve[{x'[t] == f[x[t]], x[0] == 0}, x, {t, 0, 1}][[1]]; Plot[x[t] /. sol, {t, 0, 1}] Bob Hanlon ---- Jerry <Jer75811 at yahoo.com> wrote: > Sir, I tried this and I only get plot axes, no graph. > > f[q_?NumberQ] := q > sol = NDSolve[{x'[t] == f[x[t]], x[0] == 0}, {x}, {t, 0, 1}] > Plot[x[t] /. sol, {t, 0, 1}] > > In place of {x} in sol I tried x and x[t] with no change. > In Plot I tried x instead of x[t], no help. > > Can you give me a successful example? Thanks. > > > > > David Park wrote: > > I found the answer, which is to use: > > > > f[q_?NumberQ]:= ... > > > > which prevents an initial evaluation. > > >