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 Author Comment/Response Daniele Lupo 09/27/07 06:14am Hi to all. I've a problem with a differential equation, that I'm trying to solve with mathematica 6.0.1 When I try to solve it in a symbolic way, I obtain an error \[Infinity]::indet: "Indeterminate expression \ ComplexInfinity+ComplexInfinity encountered. " Commands that I write are followings: eq = Derivative[2][f][t] + (2*l + m)*Derivative[1][f][t] + l^2*f[t] == ((m + Sqrt[m*(4*l + m)])/(2*Sqrt[m*(4*l + m)]))* Exp[(-(t/2))*((2*l + m) - Sqrt[m*(4*l + m)])] + ((-m + Sqrt[m*(4*l + m)])/(2*Sqrt[m*(4*l + m)]))* Exp[(-(t/2))*((2*l + m) + Sqrt[m*(4*l + m)])] DSolve[{eq, f[0] == 0, Derivative[1][f][0] == 0}, f, t] I know that there's a solution, so I've tried to solve it numerically, and I must to notice that, instead, NDSolve works fine: fun = f /. NDSolve[{Evaluate[eq /. {m -> .5, l -> .8}], f[0] == 0, f'[0] == 0}, f, {t, 0, 10}][[1]] Plot[fun[x], {x, 0, 10}] I obtain the right graph. Now, if Mathematica can't solve it in symbolic way, it shoud return unevaluated expression, instead of the error, right? What's wrong? There's something that I can do to solve it simbolically? Attachment: problem.nb, URL: ,

 Subject (listing for 'Problem in solving a differential equation') Author Date Posted Problem in solving a differential equation Daniele Lupo 09/27/07 06:14am Re: Problem in solving a differential equation yehuda ben-s... 09/27/07 7:24pm Re: Problem in solving a differential equation Daniele Lup 10/01/07 2:40pm
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