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Newsgroups: comp.graphics.apps.gnuplot
Date: Thu, 14 Mar 2013 10:34:10 -0700 (PDT)
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Subject: Defining multiple similar functions, and fitting them, using a for loop
From: Thomas Grant <tomer485@gmail.com>
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Xref: csiph.com comp.graphics.apps.gnuplot:1692

Dear all,

I am trying to use gnuplot to iterate through a list of data files and fit =
the data in them with a simple linear regression.  Then I would like to plo=
t all the data points and the accompanying fits on the same graph.  From th=
e help it seems like the for loop iteration only works for plotting command=
s, and not for fit.

First, I would like to fit all the data files to a function:

f1(x)=3Dm1*x+b1
f2(x)=3Dm2*x+b2
etc...

then I'd like to fit them:

fit f1(x) 'datafile_1.dat' via m1,b1
etc....

then I'd like to plot the data files, which I can do with a for loop:

plot for [i=3D1:8] 'datafile_'.i.'.dat' =20

however, I'd also like to plot the fits, which doesn't seem to work with a =
for loop.  I've tried the following (after individually defining f1(x), f2(=
x), etc...):

plot for [i=3D1:8] fi(x)
plot for [i=3D1:8] f.i.(x)
plot for [i=3D1:8] j=3Di fj(x)
plot for [i=3D1:8] j=3Di f.j.(x)
plot for [i=3D1:8] j=3Di "f".j."(x)"

and none of these seem to work.  It occurs to me it may be that gnuplot doe=
sn't seem to support the idea of defining functions with a variable, even t=
hough it would allow something such as:

plot for [i=3D1:8] j=3Di sin(i*x)

which would plot eight functions, sin(x), sin(2x), etc...

If anyone has any ideas on fitting multiple functions, I'd love to hear it.=
  Or if anyone has any ideas on defining/plotting functions with variable n=
ames, I'd also love to hear it.

If possible I would like to avoid scripting, since I would like to be able =
to make edits interactively in gnuplot, rather than editing a script, runni=
ng it, looking at the output, re-editing the script, running it, etc...=20

Thanks for your suggestions,
Tom