Re: NDSolve Singularity

*To*: mathgroup at smc.vnet.net*Subject*: [mg85552] Re: NDSolve Singularity*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Wed, 13 Feb 2008 06:57:50 -0500 (EST)*Organization*: Uni Leipzig*References*: <foucd4$l15$1@smc.vnet.net>*Reply-to*: kuska at informatik.uni-leipzig.de

Hi, if you look at your equations you see that the equation for r[t] include a term r'[t]== .. + 40.3234 * r[t] + .. and this must explode because it gives r[t] proportional to Exp[40.3234 *t] So there is only one solution .. solve other equations I would suggest {r'[t]==0,y'[t]==0} or fix you equations / parameters. Regards Jens Tara.Ann.Lorenz at gmail.com wrote: > Hello, > > The following input for NDSolve is giving me a "singularity" error > (see error message below). As a result, my system of equations is > being solved until the singularity at t=0.179 and not until t=30 as > desired. Any suggestions on how to avoid this issue? Thank you! > > va = 4.71*y[t] - 246; > q = 6; > kl = 5; > kt = 40; > b = 760; > mrco2 = 250; > caco2 = 48 + 6*(paco2 - 40)/7; > paco2 = (b - 47)*r[t]; > fico2 = 0.07; > grodinstime0to30 = > NDSolve[{r'[ > t] == (1/ > kl)*((fico2*va + 8.63*q*(y[t] - caco2)/(b - 47) - r[t]*va)), > y'[t] == (mrco2 + 10*q*(caco2 - y[t]))/(10*kt), r[0] == 0.058, > y[0] == 0.533}, {r, y}, {t, 0, 30}] > > > ERROR MESSAGE: > NDSolve::ndsz: At t == 0.17926445744166167`, step size is effectively > zero; singularity or stiff system suspected. >> > > > > > >