Re: newbie: diff equation

*To*: mathgroup at smc.vnet.net*Subject*: [mg96927] Re: newbie: diff equation*From*: dh <dh at metrohm.com>*Date*: Fri, 27 Feb 2009 06:14:44 -0500 (EST)*References*: <go63qm$q0g$1@smc.vnet.net>

Hi Mike, obviously f==0 is the correct generic solution. What you are looking for is a singular case for m== Integer. Therefore, you must give m explicitly. But then the problem is not fully specified, we may e.g. aditionally specify f'[0]: DSolve[{f''[x] == -9 f[x], f[0] == 0, f[Pi] == 0, f'[0] == 1}, f[x],x] hope this helps, Daniel 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 >