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<< Getting all solutions from DSolve >>

• To: mathgroup at smc.vnet.net
• Subject: [mg85880] << Getting all solutions from DSolve >>
• From: "Hatuey Hack" <hatuey.hack at gmail.com>
• Date: Tue, 26 Feb 2008 07:49:47 -0500 (EST)

Hello,

I am trying to solve a diffusion problem using the following equation (in
cylindrical coordinates):

DSolve[J + D*Laplacian[ns[Rr]] - ns[Rr]/\[Tau] == 0, ns, Rr]


The solution published in a scientific journal paper was:

Paper = J*\[Tau] + BesselI[0, Rr/Sqrt[D/\[Tau]]]*C[1] + BesselK[0,
Rr/Sqrt[D/\[Tau]]]*C[2]

The solution from DSolve was:

My = J*\[Tau] + BesselI[0, Rr/Sqrt[D/\[Tau]]]*C[1] + BesselY[0,
-I*Rr/Sqrt[D/\[Tau]])]*C[2]

So, the two solutions are very different, one is a real function (Paper) and
the other one is a complex function (My).

I would like to know how can I "force" DSolve to give me all the possible
solutions or at less a constrained solution (something like give me only the
real ones).

My system: Mathematica 6, Linux

Thanks in advance.

Hatuey