Re: Complexes, Reals, FullSimplify
- To: mathgroup at smc.vnet.net
- Subject: [mg48800] Re: Complexes, Reals, FullSimplify
- From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig-de>
- Date: Wed, 16 Jun 2004 07:49:02 -0400 (EDT)
- Organization: Uni Leipzig
- References: <cap3s0$cb7$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi, FullSimplify[Re[(1 - 6* I)* Cos[x] - (1 + 2*I)*Sin[0.5*x]] /. r_Real :> Rationalize[r, $MachineEpsilon], Element[x, Reals]] Regards Jens "Stergios J. Papadakis" <stergios.papadakis at jhuapl.edu> schrieb im Newsbeitrag news:cap3s0$cb7$1 at smc.vnet.net... > Dear group, > I am trying to use expressions of the below form as boundary conditions > in NDSolve. I keep getting "non-numerical" errors. I have tried a lot > of things and reduced the problem to this: > > These give different outputs: > > FullSimplify[Re[(1 - 6* I)* Cos[x] - (1 + 2*I)*Sin[(1/2)* x]],Element[x, > Reals]] > > FullSimplify[Re[(1 - 6* I)* Cos[x] - (1 + 2*I)*Sin[0.5*x]],Element[x, > Reals]] > > I get: > > \!\(Cos[x] - Sin[x\/2]\) > > Re[(1 - 6 \[ImaginaryI]) Cos[x] - (1 + 2 \[ImaginaryI]) Sin[0.5 x]] > > > I think I can get my NDSolve to work if I can make the second > FullSimplify above give me an output without an Re in it. Mathematica > assumes that 0.5 may have some tiny imaginary part and therefore keeps > everything for full generality. How do I eliminate > this? Note that I have simplified things a lot here, the actual > expression that I will be using has many terms that all have the > form above, with many significant digits, which depend on earlier > calculations. I have tried using Chop, > > FullSimplify[Chop[Re[(1 - > 6* I)* Cos[x] - (1 + 2*I)*Sin[0.5* x]]], Element[x, Reals]] > > And that does not work, I get the same result. > > > > > > > Thanks, > Stergios >