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Re: Problems with DSolve
*To*: mathgroup at smc.vnet.net
*Subject*: [mg119684] Re: Problems with DSolve
*From*: "Kevin J. McCann" <Kevin.McCann at umbc.edu>
*Date*: Fri, 17 Jun 2011 00:09:56 -0400 (EDT)
*References*: <itcd8j$cuk$1@smc.vnet.net>
Your syntax for the differential equations is incorrect. Note that you
need to have stuff == stuff. Often the second "stuff" is a zero. Also,
unless it is some copy issue, you initial conditions don't read
correctly, e.g. x[0] D. I think you mean x[0]==D. However, note that "D"
is a the name of the derivative function; so, you shouldn't use it. Use
"d" or some other. Check the Help on DSolve.
Kevin
On 6/16/2011 4:01 AM, David King 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[0] D,y[0] 0,z[0] 0},
> {x[t],y[t],z[t]},t]
>
> So far, Mathematica returns the following:
>
> Out[7]:= 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[0] D,y[0] 0,z[0] 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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