Re: Complexes, Reals, FullSimplify
- To: mathgroup at smc.vnet.net
- Subject: [mg48815] Re: [mg48782] Complexes, Reals, FullSimplify
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Thu, 17 Jun 2004 04:07:32 -0400 (EDT)
- References: <200406160854.EAA12221@smc.vnet.net> <3FF51E64-BF8F-11D8-890A-000A95B4967A@mimuw.edu.pl>
- Sender: owner-wri-mathgroup at wolfram.com
Of course I meant: ComplexExpand[Re[(1 - 6*I)*Cos[x] - (1 + 2*I)*Sin[0.5*x]]] Cos[x] - Sin[0.5*x] (that Element[x,Reals] was there only because I forgot to delete it form your original code.) Andrzej On 16 Jun 2004, at 21:18, Andrzej Kozlowski wrote: > > On 16 Jun 2004, at 17:54, Stergios J. Papadakis wrote: > >> 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 >> >> > > The simplest way is to use ComplexExpand; you do not even need > FullSimplify: > > ComplexExpand[Re[(1 - 6* I)* Cos[x] - (1 + 2*I)*Sin[0.5*x]], Element[x, > Reals]] > > Cos[x] - Sin[0.5*x] > > > Andrzej Kozlowski > Chiba, Japan > http://www.mimuw.edu.pl/~akoz/ >
- References:
- Complexes, Reals, FullSimplify
- From: "Stergios J. Papadakis" <stergios.papadakis@jhuapl.edu>
- Complexes, Reals, FullSimplify