       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, i2 == 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, i2 == 0}, {i1[t], i2[t]}, {t, 0, 1}]
>
> What is wrong?
>
> Thanks
> Chee

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