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MathGroup Archive 1999

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Re: Problem with the zero-term of Fourier[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19678] Re: Problem with the zero-term of Fourier[]
  • From: adam.smith at hillsdale.edu
  • Date: Thu, 9 Sep 1999 02:19:48 -0400
  • Organization: Deja.com - Share what you know. Learn what you don't.
  • References: <7qsftj$17c@smc.vnet.net> <7r252g$6qt@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

I downloaded your files and tried them on my machine.  (Dell Pentium II
running Windows NT 4.0 and Mathematica Version 3.0.1.1x).  My machine
is limited in memory and I did not have sufficient memory to do the
full 200,000 list - the computer kept bombing.  But I was able to
succefully get the correct result with a 100,000 element list.  So
maybe your problem is that you are right at the limits of the memory
requirements to do 200,000 elements.  Just a thought.  My run for
100,000 is included below.

Adam Smith


A Problem

6. Sep. 1999
Real Example
Read the data
In[1]:=
rawixr=ReadList["ixr.txt", Real];
Length[rawixr]
Out[1]=
200000
Note:  there seems to be some memory problem with trying to do 200,000
elements.  So try shorter "subsets"
In[2]:=
ixr = Take[rawixr,100000];
Length[ixr]
Out[2]=
100000
The Average
In[3]:=
(Plus@@ixr)/Length[ixr]
Out[3]=
-0.33816
The Zeroterm of the Fouriertransformation
Remember, that Mathematica's F-transfomation is defined by
1/Sqrt[n] ... Therefore we calculate
In[4]:=
1/Sqrt[Length[ixr]] Fourier[ixr] [[1]]
Abs[%]
Out[4]=
-0.33816+0. I
Out[5]=
0.33816



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