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tecCmd

tecCmd is a utility for generating publication quality plots effortlessly. I wrote the script around 2018. I used it extensively during my PhD.

I was using gnuplot initially for plotting data. Gnuplot is excellent. But the output files are not suitable for directly putting into publications. An another plotting software is Tecplot. It is extensively used in the field of computational fluid dynamics for visualization. Around 2018, Tecplot released a python API for their Tecplot-360. This means that we need not launch a GUI to plot data. The command line utilities are much more memory efficient. They also open up opportunities for automation using simple bash scripting. A Python API together with evil eval can be exploited for data manipulation.

Features:

  • Generate tecplot layout files using simple and intuitive scripting similar to gnuplot (see examples below)
  • Column data can be manipulated in an arbitrary fashion, limited only by the capabilities of Python expression evaluation engine.
  • Low memory footprint. Launching Tecplot over SSH is remarkably slow. You can instead write a simple script and directly generate the postscript files.

It gets the job done. I wrote it on a Friday evening.

Examples

See the examples directory for the input data files.

Example 1

Reading matrix from data.txt and plotting column 1 on x-axis and column 2 on y-axis.

gnuplot tecCmd 
set terminal postscript color
set out 'gnuplot.ps'
plot 'data.txt' u 1:2
set out



set out 'tecCmd.ps'
plot 'data.txt' u 1:2
set out

Example 2

Using functions to transform the input matrix columns. In this example, I am reading matrix from data.txt, plotting column 1 on x-axis, and sin(pi$1)* on the y-axis. The syntax convention is close to gnuplot. Functions defined in numpy are available in global namespace and can be evaluated.

gnuplot tecCmd 
set terminal postscript color
set out 'gnuplot.ps'
set xrange [0:3.14]
set yrange [-1:1]
plot 'data.txt' u 1:(sin(pi*$1)) w l
set out



set out 'tecCmd.ps'
set xrange [0:3.14]
set yrange [-1:1]
plot 'data.txt' u 1:(sin(pi*$1)) w l
set out

Example 3

Using user defined functions to transform the input matrix columns. Everything that appears after keyword is passed to exec

gnuplot tecCmd 
set terminal postscript color
set out 'gnuplot.ps'
set xrange [0:3.14]
set yrange [-1:1]
f(x) = sin(pi*x)
plot f(x) w l
set out



set out 'tecCmd.ps'
set xrange [0:3.14]
set yrange [-1:1]
keyword f=lambda x: sin(pi*x)
plot function("(x): return vstack((x, f(x))).T") u 1:2 w l
set out

Example 4

Plot multiple lines: Legendre Polynomials.

gnuplot tecCmd 
set terminal postscript color
set out 'gnuplot.ps'
set xrange [-1:1]
set yrange [-1:1]
P0(x) = 1
P1(x) = x
P2(x) = 0.5*(3*x**2-1)
P3(x) = (35*x**4-30*x**2+3)/8.
P4(x) = (63*x**5-70*x**3+15*x)/8.
plot P0(x) w l lc 'red' t 'P0', \
     P1(x) w l lc 'green' t 'P1', \
     P2(x) w l lc 'blue' t 'P2', \
     P3(x) w l lc 'orange' t 'P3', \
     P4(x) w l lc 'magenta' t 'P4'
set out



set out 'tecCmd.ps'
set xrange [-1:1]
set yrange [-1:1]
keyword x=linspace(-1,1)
keyword P0=lambda x: (x+1-x)
keyword P1=lambda x: x
keyword P2=lambda x: 0.5*(3*x**2-1)
keyword P3=lambda x: (35*x**4-30*x**2+3)/8.
keyword P4=lambda x: (63*x**5-70*x**3+15*x)/8.
plot function("(x): return vstack((x, P0(x))).T") u 1:2 w l lc 'red' t 'P0', \
     function("(x): return vstack((x, P1(x))).T") u 1:2 w l lc 'green' t 'P1', \
     function("(x): return vstack((x, P2(x))).T") u 1:2 w l lc 'blue' t 'P2', \
     function("(x): return vstack((x, P3(x))).T") u 1:2 w l lc 'orange' t 'P3', \
     function("(x): return vstack((x, P4(x))).T") u 1:2 w l lc 'magenta' t 'P4'
set out

Example 5

Sometimes we have log files. Bash utilities are useful for analyzing log files. This example shows how to execute bash command, and utilize the output to plot data.

gnuplot tecCmd 
set terminal postscript color enhanced
set out 'gnuplot.ps'
set datafile separator ","
set logscale y
set xlabel 'Non-dimensional time: t/t_0'
set ylabel 'Residual: |f^{n+1} - f^{n}|/|f^{n}|'
set key at 85,85
set yrange [1e-9:1e-3]
set xrange [0:6]
set xtics 0,1,6
plot "<grep 'dgfsresidualstd' data.txt | cut -d ':' -f2-" u 1:2 w l lc 'red'
set out



set out 'tecCmd.ps'
set datafile separator ","
set logscale y
set xlabel 'Non-dimensional time: t/t<sub>0</sub>'
set ylabel 'Residual: |f<sup>n+1</sup> - f<sup>n</sup>|/|f<sup>n</sup>|'
set yrange [1e-9:1e-3]
set xrange [0:6]
set xticks spacing 1
plot system("grep 'dgfsresidualstd' data.txt | cut -d ':' -f2-") u 1:2 w l lw 0.3 lc 'red'
set out
See example 6 which modifies gnuplot script to mimick the tecCmd output.