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not linear homogeneus differential equation system... too complicated for mathmeatica... maybe only for me! :)

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  • Subject: [mg41718] not linear homogeneus differential equation system... too complicated for mathmeatica... maybe only for me! :)
  • From: "Alessandro" <TheOpps75 at yahoo.it>
  • Date: Mon, 2 Jun 2003 04:35:24 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

For the type of system I'm studing I guess the system of differential
equation (not liear) I'm going to asking about should have solution.
Unfortunatly my knoledge about mathmatica is very poor, seems to be a bit
too complicated to try with paper and pencil in a reasoneble time, and so
I'd like to have some help.
The Mathematica cell is:


DSolve[
    {     s'[t] == -A*s[t] +B*u[t],
           u'[t] == A*s[t] - (E + C*a[t] + B)*u[t],
           a'[t] == F*b[t] - C*a[t]*u[t],
           b'[t] ==  C*a[t]*u[t] - (G + F)*b[t],
           s[0] == s0, a[0] == a0, b[0] == 0,   u[0] == 0},
    {s[t], u[t], a[t], b[t]}, t]

I have two problem:
1) Before I was considering C=C' 1/a[t]... the system was linear and
solvable. Nevertheless the solution was a very long formula. I needed to
compact the result with FullSimplify. Is it the right way or I can feed
DSolve with some option in order to get a compact result by default?
2)  Later I realized I was solving the erroneous equations. This new non
linear system is solved by Mathematica, after some minutes (CPU 2GHz 512Mb),
Mathematica answer with the same input I gave as output... well... I think
it is not able to solve it. There is some mathematica toolbox or some way to
solve it. It is probable I wiil need to change other things in the equation
so I'd prefer some suggestion in order to understand what to do instead of
the raw solution... however I will not disregard a solution :))))

Wow... too long... for a question probable will not interess  too much
people... sorry

Thanks
Ale



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