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MathGroup Archive 1999

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Re: HELP: Plotting composite functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg16067] Re: [mg15946] HELP: Plotting composite functions
  • From: "Tomas Garza" <tgarza at mail.internet.com.mx>
  • Date: Tue, 23 Feb 1999 03:45:21 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

Alexander Sirotkin wrote:

>Simple question - after definition of a functions
>which looks like this "H[w] == Log[10, 1 + Exp[I2Pi w]]"
>I try to Plot[] it and get the "... not machine size real
>number at ..." error. After reading lots of manuals and
>postings I came to a conclusion that it should be somehow
>related to Evaluate[]/Hold[] problems, but none of these
>manuals gave a solution to this problem.

Alexander,

First, you have to use := instead of == in order to define your function H
(I suppose there was a misprint in your message).

Second, your definition requires a "_" to be written after the argument,
i.e.

H[w_]:=Log[10, 1 + Exp[I2Pi w]]

Third, it is clear that Exp[I2Pi w] is not real and hence cannot be plotted
as such.

If you want to have visual information about the behavior of the complex
exponential try plotting its absolute value or its real and imaginary
values. E.g.,

Plot[Abs[H[x]],{x,1,2},PlotRange->{{1.46,1.54},{1,3}}]

looks real nice.

Good luck,

Tomas Garza
Mexico City



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