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Re: Difficulties with Re

  • To: mathgroup at
  • Subject: [mg98326] Re: [mg98349] Difficulties with Re
  • From: Curtis Osterhoudt <cfo at>
  • Date: Wed, 8 Apr 2009 02:43:19 -0400 (EDT)
  • Organization: LANL
  • References: <>
  • Reply-to: cfo at

On Monday 06 April 2009 03:05:13 am Aaron Fude wrote:
> Assuming[x > 0 && y > 0, Re[Exp[x + I y]] // Simplify]
> Assuming[x > 0 && y > 0, Re[Exp[(x + I y)^2]] // Simplify]

Hi, Aaron, 

   If you check the expansion of the second expression, you'll notice that it contains a part proportional to Exp[2ix*y]. This is generally complex for x>0 and y>0; if x*y is an integer multiple of pi, then the entire expression reduces to a real number; otherwise, the whole expression is imaginary. Unless you provide Mathematica (or anyone) more constraints on x and y, there is no way to tell you whether the whole thing has a real part, or whether the real part is zero. 

Curtis Osterhoudt
cfo at
PGP Key ID: 0x4DCA2A10

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