Re: Some problems with DSolve and NDSolve

*To*: mathgroup at smc.vnet.net*Subject*: [mg19775] Re: Some problems with DSolve and NDSolve*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Fri, 17 Sep 1999 01:36:36 -0400*Organization*: Universitaet Leipzig*References*: <7rnjb1$ejs@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, the system is singular, Mathematica can't find two explicit differential equations for i1'[t] und i2'[t]. Your equations say that deltaI'[t]=i2'[t]-i1'[t] is given by 2 i1[t] - 2 deltaI'[t] == 80 t E^(-2t), 4 i2[t] + 2 deltaI'[t] == 0 Hope that helps Jens Chee Lim Cheung wrote: > > Hi MathGroupers, > > I was somewhat surprised that DSolve is unable to solve the following > relatively innocuous system of 1st-order ODEs: > > DSolve[{2 i1[t] + 2 (i1'[t] - i2'[t]) == 80 t E^(-2t), 4 i2[t] + 2 (i2'[t] > - i1'[t]) == 0, i1[0] == 0, i2[0] == 0}, {i1[t],i2[t]}, t] > > The normally reliable NDSolve also falls down on the following: > > NDSolve[{2 i1[t] + 2(i1'[t] - i2'[t]) == 80 t E^(-2t), 4 i2[t] + 2(i2'[t] - > i1'[t]) == 0, i1[0] == 0, i2[0] == 0}, {i1[t], i2[t]}, {t, 0, 1}] > > What is wrong? > > Thanks > Chee