Re: not linear homogeneus differential equation system... too complicated for mathmeatica... maybe only for me! :)
- To: mathgroup at smc.vnet.net
- Subject: [mg41729] Re: [mg41718] not linear homogeneus differential equation system... too complicated for mathmeatica... maybe only for me! :)
- From: Selwyn Hollis <selwynh at earthlink.net>
- Date: Tue, 3 Jun 2003 07:13:11 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
On Monday, June 2, 2003, at 04:35 AM, Alessandro wrote: > 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? DSolve followed by Simplify or FullSimplify is probably the right thing to do. > 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 :)))) You'll have to settle for a numerical solution using NDSolve. Of course this will require specific values for the coefficients. ----- Selwyn Hollis http://www.math.armstrong.edu/faculty/hollis