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Re: newbie: diff equation

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  • Subject: [mg96927] Re: newbie: diff equation
  • From: dh <dh at>
  • Date: Fri, 27 Feb 2009 06:14:44 -0500 (EST)
  • References: <go63qm$q0g$>

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


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