Date: Apr 10, 2013 2:44 AM
Author: Torsten
Subject: Re: Solving an unusual system of ODES
D R G <grimesd2@gmail.com> wrote in message <ea631802-c941-4e78-9832-3561e21842bf@googlegroups.com>...

>

> On Tuesday, April 9, 2013 2:15:07 PM UTC+1, Torsten wrote:

> > D R G <grimesd2@gmail.com> wrote in message <5c502161-10e9-4863-9e76-57617f33fb35@googlegroups.com>...

> >

> > > Yes, that is what I want to solve; however, the case you're referring to is I believe the trivial case; we have already solved for when k = 0, and got a non-trivial solution. As K is small, this will be close to it and there will be non zero solutions.

> >

> > >

> >

> > > Regards

> >

> > >

> >

> > > DRG

> >

> > >

> >

> >

> >

> > No, y=0 is the only solution that satisfies your differential equation together with the two boundary conditions - also for the case K and/or J not equal to 0.

> >

> > You will have to change the boundary conditions to get a solution different from y=0.

> >

> >

> >

> > Best wishes

> >

> > Torsten.

>

> Hmm.. that is quite unexpected! Alright, so can we extend this for the case

>

> C(RN) = 0

> dC/dr (RN) =! 0 ?

>

> Thanks in advance

>

> DRG

In the case dC/dr (RN) not equal to 0 you will get a nontrivial solution.

When you use ODE45 to solve, just interpret the time variable as the space variable:

dX(1) = X(2)

dX(2) = J*X(1)/(X(1) + K) - 2/t*X(2)

Usually stationary second-order ODEs are boundary value problems - i.e. one boundary condition is given at RN and the second at RO. Are you sure the physics of your problem leads to two boundary conditions at RN ?

Best wishes

Torsten.