Re: New to mathematica: Question about solving
- To: mathgroup at smc.vnet.net
- Subject: [mg74692] Re: [mg74664] New to mathematica: Question about solving
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Sat, 31 Mar 2007 01:38:17 -0500 (EST)
- Reply-to: hanlonr at cox.net
soln=DSolve[{y'[x] == y[x] + y[x]^3}, y[x], x] {{y[x] -> -((I*E^(x + C[1]))/ Sqrt[-1 + E^(2*x + 2*C[1])])}, {y[x] -> (I*E^(x + C[1]))/Sqrt[-1 + E^(2*x + 2*C[1])]}} soln=soln/.{ expr1_*(expr2_)^(-1/2):>(expr2/(expr1^2))^(-1/2), C[1]:>-Log[C]/2}//ExpandAll {{y[x] -> 1/Sqrt[C/E^(2*x) - 1]}, {y[x] -> 1/Sqrt[C/E^(2*x) - 1]}} Bob Hanlon ---- traz <t_raz at yahoo.com> wrote: > Whenever I try to solve differential equations in mathematica, I get a solution with an imaginary part different from the solution in a text book. For example: > > DSolve[{y'[x] == y[x] + y[x]^3}, y, x] > > will give me a solution that has an imaginary part and not the one I expect here from the text book: > > {+(Ce^(-2x)-1)^(-1/2), -(Ce^(-2x)-1)^(-1/2)} > > Can anyone give me a tip on how to do this? Also does anyone know of an online tuttorial that goes into details a little bit? >