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. >