TetaTricks/chap/gnuplot.tex

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% nouveau 27 septembre 2020
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\chapter{Gnuplot}
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\index{Gnuplot}\label{chap:gnuplot}
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Gnuplot - an interactive plotting program
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There is an on-line demo collection at http://gnuplot.info/demo
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\section{Exemple : le phytotron}
\index{phytotron}
\begin{verbatim}
#!/bin/bash
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# THIS IS A KLUDGE
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nbsamp=3000 # nombre d'echantillon
if [ $# -eq 1 ]; then
nbsamp=$1
fi
DATAFILE="serial/foo.dat"
IMAGE="graphe.png"
TMPFILE="/dev/shm/tmpdata"
tail -${nbsamp} < ${DATAFILE} > ${TMPFILE}
gnuplot << __EOC__
set term png size 1600,800
set output "${IMAGE}"
set ytics 2
set xtics
set grid front
set title "* Temperatures du Phytotron *"
set xdata time
set timefmt "%s"
set format x "%b %d\n%H:%M"
set yrange [ 10.0 : 40.0 ]
plot "${TMPFILE}" using 1:3 title " inside" with lines, \
"${TMPFILE}" using 1:4 title "ambient" with lines
__EOC__
display ${IMAGE} &
\end{verbatim}
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\section{Questions}
Supposons que nous ayons sous le coude un fichier contenant
\emph{six cent mille} lignes de données, qui ne représentent que
trente secondes d'enregistrement d'une valeur de Virgo\index{Virgo},
comment faire pour plotter les échantillons $N$ à $N+42$ ?
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