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MathGroup Archive 1999

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RE: HELP : Mathematica v4 producing erroneous results ! Mathematica3 worked fine...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18989] RE: [mg18954] HELP : Mathematica v4 producing erroneous results ! Mathematica3 worked fine...
  • From: "Ersek, Ted R" <ErsekTR at navair.navy.mil>
  • Date: Tue, 3 Aug 1999 13:44:35 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

slinger at signal.dera.gov.uk  wrote:
-------------------------------------

We recently upgraded to Mathematica v4 on NT and Solaris from Mathematica
v3.
To my horror, I discovered that notebooks which produced good results under
3 produced
errroneous ones under v4.

I have traced the fault, and the code below is distilled down to illustrate
the
problem.  Basically, I'm simply assigning complex numbers to an array using
a
Do[] (but note the Fourier[], which seems to be necessary to cause the bug,
for
some reason).  Unfortunately, the imaginary parts of the result are not
correct
- their values should be as in the array "ideal" but are simply equal to the
real parts !!

-----------------------------

I deleted the original code and provide simpler code that causes the
problem.  I agree that it only comes out wrong when using Fourier.  I can't
imagine what Fourier would have to do with it!


In[1]:=
$Version

Out[1]=
4.0 for Microsoft Windows (April 21,1999)

In[2]:=
ideal={0.337385 + 0.6624I, 0.563615 - 0.750732I,
   0.869075 + 0.200504I, 0.516709 + 0.938178I};
output=Fourier[ideal]

Out[3]=
{1.14339 + 0.525175 I, 0.57861 + 0.254401 I, 
 0.063068 + 0.337729 I, -1.1103 + 0.207495 I}

In[4]:=
output[[1]]=ideal[[1]];
output

Out[5]=
{0.337385 + 0.337385 I, 0.57861 + 0.254401 I,
 0.063068 + 0.337729 I, -1.1103 + 0.207495 I}

------------------------
Part[output,1] above should be (0.337385 + 0.6624 I).

How Bizarre!
  Ted Ersek


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