NDSolve::ndsz
- To: mathgroup at smc.vnet.net
- Subject: [mg123856] NDSolve::ndsz
- From: Gausstein <gausstein at gmail.com>
- Date: Fri, 23 Dec 2011 07:13:56 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
Greetings, I have a problem solving two coupled differential equations using NDSolve. The following message appears: "NDSolve::ndsz: At t == -0.008080592178665635`, step size is effectively zero; singularity or stiff system suspected. >>" Can NDSolve actually solve these equations? or should I better try another program? I have tried everything!!! I just need to know if it is possible to solve this equations with Mathematica. The code used is the following: ********************************************************************************************************* H0 = 1/5000000; m = 3/500000000; A = 1/10^2; V0 = 3 H0^2; V0a = V0 - 1/2 A m^2 (2^(2 - 18 (1 - (7 Sqrt[51])/50)) 5^(2 - 21 (1 - (7 Sqrt[51])/50))); ti = -(11/10); tf = -Exp[-10]; V[t_] := V0 + 1/2 m^2 phi[t]^2 + UnitStep[t + 1] (-V0 + V0a + 1/2 A m^2 phi[t]^2) value1 = 2^(1 - 21/2 (1 - (7 Sqrt[51])/50)) 5^(1 - 12 (1 - (7 Sqrt[51])/50)) 11^(3/2 (1 - (7 Sqrt[51])/50)); value2 = -3 2^(1 - 21/2 (1 - (7 Sqrt[51])/50)) 5^(2 - 12 (1 - (7 Sqrt[51])/50) ) 11^(3/2 (1 - (7 Sqrt[51])/50) - 1) (1 - (7 Sqrt[51])/50); temp = NDSolve[{ Derivative[1][a][t]/a[t]^2 ==Sqrt[1/3 (1/2 (Derivative[1][phi][t]/ a[t])^2 +V[t])], Derivative[2][phi][t] + 2 Derivative[1][a][t]/a[t] Derivative[1][phi] [t] + m^2 a[t]^2 phi[t] (1 + A UnitStep[t + 1]) == 0, a[ti] == -1/(H0 ti), phi[ti] == value1, phi'[ti] == value2}, {a, phi}, {t, ti, tf}, MaxSteps -> \[Infinity], InterpolationOrder -> All] *************************************************************************************************************** I know it looks pretty messy, but once it is copied into the Notebook (and if it is converted into StandardForm) it gets clearer. I really need help!!!!!!!!!!!!!!!!!! Thanks a lot!!!