Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
1995
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 1995

[Date Index] [Thread Index] [Author Index]

Search the Archive

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] == 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
  • Next by thread: Re: Thank you very much for your answer :-)