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From: =?ISO-8859-1?Q?Oliver_G=F6tze?= <goetze.oliver@googlemail.com>
Newsgroups: comp.graphics.apps.gnuplot
Subject: Multible Fits using the same fit function lead to ?false? results.
Date: Tue, 17 May 2011 15:04:47 -0700 (PDT)
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Xref: x330-a1.tempe.blueboxinc.net comp.graphics.apps.gnuplot:315

Hi
i just noticed that using a gnuplot script like this:
fit a0 + a1*(1/x)**2 + a2*(1/x)**4\
'<grep -v \# table.dat  |awk "\$1 =="10" {print 1,\$2} \
\$1 =="10" {print 2, \$3}\
\$1 =="10" {print 3, \$4}\
\$1 =="10" {print 4, \$5}"'via a0,a1,a2
print "value a0 ",a0

fit a0 + a1*(1/x)**2 + a2*(1/x)**4\
'<grep -v \# table.dat  |awk "\$1 =="20" {print 1,\$2} \
\$1 =="20" {print 2, \$3}\
\$1 =="20" {print 3, \$4}\
\$1 =="20" {print 4, \$5}"'via a0,a1,a2
print "value a0 ",a0

fit a0 + a1*(1/x)**2 + a2*(1/x)**4\
'<grep -v \# table.dat  |awk "\$1 =="30" {print 1,\$2} \
\$1 =="30" {print 2, \$3}\
\$1 =="30" {print 3, \$4}\
\$1 =="30" {print 4, \$5}"'via a0,a1,a2
print "value a0 ",a0

on a table.dat file like this (just an example):
#x     y1     y2     y3
10     12     43     42
20    234    324   33
30     3         3       3

leads to false results, i have to reset (or set to zero) die
coefficients a0, a1, a2 after/before every fit by placing
a0=0
a1=0
a2=0
before each fit block in the gnuplot script.
If i do not do this the last values for the coefficients are taken
into the next fit and this is influencing the results.

The problem is the influence, because i do not know why this is so,
and setting them to zero is just one way i could use other values too!