Re: Solve / NSolve take too much time or fail

*To*: mathgroup at smc.vnet.net*Subject*: [mg60874] Re: Solve / NSolve take too much time or fail*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Sat, 1 Oct 2005 02:55:49 -0400 (EDT)*Organization*: The Open University, Milton Keynes, U.K.*References*: <dhirn9$ltd$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

grimey wrote: > Hello, > I'm working with Mathematica (version 5.0) for perhaps 3 month. > And now I have a problem, I try to solve an equation like this: > > cf=(a1*x (a2 + a3*x + a^2))/(b1 + b2*x - b3*x^2 + b4*x^3); > > w=(1-c1*Sqrt[1-(1-c1^2)*x/c2])^2 / (1-c1)^2; > > This is the main equation: > > Solve[Numerator[cf]-I d1 w Denominator[cf]==0,x] > > And even after hours of working I don't get any solution, whether I > take Solve or NSolve. And I gave a lot of virtual memory free for > Mathematica to work with. > > Are there any tricks to help solving difficult polynomial equations > faster (or at all)? I want to get, of course, a set of Root-functions > for x (complex), depending on a1, a2, a3, b1, b2, b3, b4, c1, c2, d1, > so I have no numerical number to start with for the FindRoot-function. > Can anyone help me? Some other equations, not always that different > from this one, could be solved more easily... > > Thank you very much! > > Thomas Geyer > (tfgeyer at yahoo.com) > Hi Thomas, I tried your equation with Mathematica 5.2 for Windows (Pentium IV 2.6 GHz, 512 Mo), first with Solve then with Reduce, but I eventually abort both commands after more than two hour of processing (elapsed time). However, I got the answer using another CAS (I sent a private email with a MS Word document containing the solution). Best regards, /J.M.