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}] =============================================