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MathGroup Archive 1999

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Re: Plot[] problem (plnr) - help !!!

  • To: mathgroup at smc.vnet.net
  • Subject: [mg15992] Re: [mg15935] Plot[] problem (plnr) - help !!!
  • From: "Richard Finley" <rfinley at medicine.umsmed.edu>
  • Date: Fri, 19 Feb 1999 03:27:08 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

Alexander,

It is not clear to me what you are trying to do??  I presume you mean to 
use the assignment operator = instead of the comparator ==??  If 
that is true, and I presume you meant to put the Clear[H] before you 
define H rather than after??  Even so, you will not be able to plot the 
function as is since it has real and imaginary parts.  Instead try this:
a[0]=1
a[1]=.99/50000
H[w_]:= Log[10,Sum[a[k] Exp[I 2 Pi w(-k)], {k,0,1}]]
Plot[Abs[H[w],{w,1,100}]

or you could plot the Real and Imaginary parts separately.  Regards, RF

>>> Alexander Sirotkin <root at borjch.math.tau.ac.il> 02/17/99 10:34PM >>>
Hi.

I'm trying to do most trivial and simple thing - define
some function and then Plot[] it. However, I get some very
weird error - "  ...is not a machine-size real number at ..."

Here is the code :
a[0]==1
a[1]==0.99/50000
H[w] == Log[10,Sum[a[k] Exp[I 2Pi w(-k)], {k,0,1}]]
Clear[H]
Plot[H[w], {w, 1, 100}]

I've seen some articles (even at www.wolfram.com) about that
problem, but NONE of them proposed a working solution !!!

Just putting Evaluate[] inside the Plot[] does nothing...




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