Re: NDSolve problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg31817] Re: NDSolve problem*From*: Roland Franzius <Roland.franzius at Uos.de>*Date*: Wed, 5 Dec 2001 06:51:39 -0500 (EST)*Organization*: Uni Osnabrueck*References*: <9u4gqb$lpb$1@smc.vnet.net> <9ua1tk$13v$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

If the system of ODE's has a critical point somewhere, say at x=a, it should always be possible, to extract the singularilty by the ansatz of critical exponents y_i = (x-a)^(s_i) z_i(x), i=1,..n in such a way that the resulting system for z is smooth or L^1 or something like that. At least one solution should be well behaved at this point then. Jens-Peer Kuska wrote: > Hi, > > your system of equations has a singularity at this point > and one of the components goes to infinity. The stepsize > control detect the singularity and reduce the stepsize > until it is to small. > > You should care full analyse the differential equation > if the singularity is not expected/obvious. > > With an ordinary differntial equations solver it is > impossible to jump over the singularity, because > the most ode solver use a polynomial approximation > to the solution and you can't approximate 1/x with > a polynomial of positive powers. > > Regards > Jens > > deniz.seker at arcelik.com.tr wrote: > > > > Hi, > > > > I have a problem with NDSolve. I'm trying to solve 2 coupled differential > > equations. But dur,ng the solution, I saw a message that,"At t=.... step > > size is effect,vely zero, singularity suspected." Then, I'm trying to > > decrease StartingStepSize option up to 10^(-14) or increase MaxSteps to > > 100000. But, for these two cases, I couldn't get solutions for 6 hours run. > > What should I do? > > > > Best regards, > > > > Deniz > > > > PS : If anybody wants to see the notebook, I can send via e-mail. -- Roland Franzius