       Help with NDSolve

• To: mathgroup at christensen.cybernetics.net
• Subject: [mg1525] Help with NDSolve
• From: imm at cs.umd.edu (Ibrahim Matta)
• Date: Sun, 25 Jun 1995 02:09:31 -0400
• Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742

```[You may get two copies of this message. - moderator]

I am trying to solve a differential equation
NN'[t] = lambda ( 1 - B[t] ) - mu NN[t]
where B[t] is a fixed point of a function of NN[t] and B[t].

The program below does not, however, terminate.
It works if we use Nest instead of FixedPoint, but
we need FixedPoint for the stopping criteria.
I suspect that with FixedPoint Mathematica can not
symbolically get the differential equations.
Is there a way around this or it can't be done with
Mathematica ?

Any help is very much appreciated.

Best regards,
Ibrahim

=============================================

T = 20
lambda = 0.8
mu = 1.0
K = 2

Clear[NN]
Clear[B]

B[b_] := (NN[t] / (1 - b))^K / K! /
(1 + Sum[(NN[t] / (1 - b))^ii / ii!, {ii, K}])

sol = NDSolve[{NN'[t] ==
lambda (1 - FixedPoint[B, 0.1, SameTest->(Abs[#1 - #2] < 10.^-4 &)])
- mu NN[t], NN == 0},
NN, {t, T}]

Plot[Evaluate[NN[t] /. sol], {t, 0, T}]

=============================================

```

• Prev by Date: Re: Fitting data on a vertical line
• Next by Date: Re: Implicit surface plotting
• Previous by thread: Re: Help with NDSolve