GNU Plot Tricks

Bar-n

In GNU Plot, if you want the figure has the labelled axis, you can always use the set xlabel or set ylabel command. However, if you want to have the label more fancy, you need to consult the ps_guide.ps and then to see which fancy symbols you want to use. So far, postscript enhanced terminal is the only flexible terminal for plotting.

In the ps_guide, it said @ means to align the superscripts and subscripts, however, it is wrong! The @ symbol actually means to place the next symbol (or block of symbols) without allocating spaces. Hence the forthcoming symbols will occupy the same place with this one. Take bar-n (i.e. \(\bar{n}\)) as an example, the “bar” bears the code 305 (octal) in Times font, so this command will put bar-n as the y-axis label:

set ylabel {/Times-Roman @{\305\305}n}

I need two 305 because the bar is rather short, so I need two to cover the whole n.

Polar polt

Easy, issue these commands first:

set polar
set grid polar
set angle radians

then use t as the radian angle and plot for r(t)

Argand Diagram

Plotting complex numbers in the form of argant diagram can be done in the following way. Firstly, declare parametric plot (set parametric). Secondly, define a complex function. The imaginary number is written as {0,1}. Thirdly, plot the complex function by obtaining argument and magnitude via arg() and abs() functions. The following is an example for plotting \(g(\omega)=\frac{k}{j\omega(-\omega^2+j\omega+4)}\) with different values of \(k\),

unset border
set angles radians
unset key
set parametric
set samples 50000, 50000
set xzeroaxis
set yzeroaxis
set xtics axis
set ytics axis
g(w,k)=k/(w*{0,1}*(-w**2+w*{0,1}+4))
paramx(t,k)=abs(g(t,k))*cos(arg(g(t,k)))
paramy(t,k)=abs(g(t,k))*sin(arg(g(t,k)))
plot [t=0:1000] [-1.5:0.5] [-1.5:0.5] \
  paramx(t,1),paramy(t,1) , \
  paramx(t,3),paramy(t,3) , \
  paramx(t,3.5),paramy(t,3.5) , \
  paramx(t,4),paramy(t,4)