Complexes, Reals, FullSimplify

*To*: mathgroup at smc.vnet.net*Subject*: [mg48782] Complexes, Reals, FullSimplify*From*: "Stergios J. Papadakis" <stergios.papadakis at jhuapl.edu>*Date*: Wed, 16 Jun 2004 04:54:52 -0400 (EDT)*Organization*: Johns Hopkins University Applied Physics Lab, Laurel, MD, USA*Sender*: owner-wri-mathgroup at wolfram.com

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

**Follow-Ups**:**Re: Complexes, Reals, FullSimplify***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>