       Re: Problems with DSolve

• To: mathgroup at smc.vnet.net
• Subject: [mg119696] Re: Problems with DSolve
• From: michael partensky <partensky at gmail.com>
• Date: Fri, 17 Jun 2011 05:52:15 -0400 (EDT)
• References: <201106160801.EAA13245@smc.vnet.net>

```Your equations are incorrect; there is no equal (==) sign.
This is kind  like  asking Mathematica to solve x-2 instead of x-2 ==0.

On Thu, Jun 16, 2011 at 4:01 AM, David King <drdavidbking at gmail.com> wrote:

> Hello Mathematica Forum,
>
> I am a new forum contributer, so it is nice to meet you.  I was hoping
> at least one of you could help me out.  I am attempting to find an
> exact solution to a system of differential equations
>
> I  type in the following Dsolve  function:
>
>  sol=DSolve[{x'[t] -(0.355+(0.645t/(t+223.06)))x[t]+0.311y[t]
> +0.046z[t] - 0.149x[t] -0.259x[t],y'[t] 0.149x[t] -
> 0.311y[t],z'[t] 0.259x[t] -0.046z[t],x D,y 0,z 0},
> {x[t],y[t],z[t]},t]
>
> So far, Mathematica  returns the following:
>
> Out:=  DSolve[{x=A2[t] -0.408 x[t]+(-0.355-(0.645 t)/(223.06 +t)) x[t]
> +0.311 y[t]+0.046 z[t],y=A2[t] 0.149 x[t]-0.311 y[t],z=A2[t] 0.259
> x[t]-0.046 z[t],x D,y 0,z 0},{x[t],y[t],z[t]},t]
>
> Which is what my question is.... This is kind of like asking  "Who's on
> first?"  and mathematica answers:  "Who's on first."  Which is what my
> question is....  I am pretty sure that my syntax is correct.  Anyway,
> I was hoping that you might be able to knock this one out of the
> park.
>
> I have a numerical solution, just not an exact solution.
>
>

```

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