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MathGroup Archive 2009

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Does FindFit really use Norm[] when NormFunction -> Norm?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg98344] Does FindFit really use Norm[] when NormFunction -> Norm?
  • From: Szabolcs <szhorvat at gmail.com>
  • Date: Wed, 8 Apr 2009 02:46:33 -0400 (EDT)

Today there was a question about fitting complex valued functions
again.  It's not difficult to find the answer on MathGroup (posted by
Darren Glosemeyer):

http://groups.google.com/group/comp.soft-sys.math.mathematica/msg/d31cd1dd0cb8519b

But something doesn't seem to be right here ... Doesn't Norm[] return
a real number, so isn't Abs at Norm[...] really the same as Norm[...]?  I
vaguely remembered that I already asked about this, and managed to
find the relevant thread:

http://groups.google.com/group/comp.soft-sys.math.mathematica/browse_thread/thread/24d2cad540e63729/dce449ac84966959

But no one has given a definite reply there.  So I'll ask again:  What
going on?  Why does FindFit[..., NormFunction -> Norm] behave
differently from FindFit[..., NormFunction -> myNorm] when myNorm is
defined as myNorm[x___] := Norm[x]?

Szabolcs


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