Re: newbie: diff equation

• To: mathgroup at smc.vnet.net
• Subject: [mg96917] Re: newbie: diff equation
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Fri, 27 Feb 2009 06:12:50 -0500 (EST)
• Organization: Uni Leipzig
• References: <go63qm\$q0g\$1@smc.vnet.net>

```Hi,

you  can't, because this is a eigenvalue problem and *not* a
differential equation. An eigenvalue problem has either none or
an infinite number of solutions and Mathematica gives you
the "none" solution, especial because it would take to long
to print out the infinite number of solutions.

In QM you take one of the infinite solutions and normalize it.
And you have to do it manual in Mathematica.

Regards
Jens

Mike wrote:
> My problem is very simple, I'm sure someone can help me out quickly. I am trying to solve some systems of differential equations a bit like a particle in a box (QM) so I started with this basic problem which I know how to solve just to make sure I am entering everything ok, but I can't even get it to work.
>
> I want to solve f''[x]= - m^2 f[x]
>
> with f[0] = 0 and f[Pi] = 0
>
> this is obviously only solvable with the condition on m being integer but if I do DSolve on the above with the boundary conditions I just get f=0. How can I get mathematica to solve this and give me the conditions on m? I need to solve much more general problems of this type. I hope someone can help.
> Many thanks
>

```

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