Re: NDSolve error message: Can't find starting value ...

*To*: mathgroup at smc.vnet.net*Subject*: [mg23799] Re: NDSolve error message: Can't find starting value ...*From*: "Bill Bertram" <wkb at ansto.gov.au>*Date*: Sat, 10 Jun 2000 02:59:55 -0400 (EDT)*Organization*: Australian Nuclear Science and Technology Organisation*References*: <8hfggl$i4h@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Axel Kowald <axel at itb.biologie.hu-berlin.de> wrote in message news:8hfggl$i4h at smc.vnet.net... > Hello, > > I try to solve the following second order ODE with NDSolve > > NDSolve[{0 == R''[x] + DiracDelta[x] - R[x], R''[-3] == 0, > R''[3] == 0}, R, {x, -3, 3}] > > and I get the following error message: > Axel, Using the equivalent boundary conditions R[-3] == 0 and R[3] == 0, Mathematica (V4.0) comes up with the numerical solution, R[x] = 0 everywhere which is wrong, but not really surprising. However try DSolve instead of NDSolve e.g. DSolve[{0 == R''[x] + DiracDelta[x] - R[x], R [-3] == 0, R [3] == 0}, R[x], x] This will give you the analytic solution which, as far as I can tell, seems correct. Cheers, Bill