The following plot styles allow arrows or lines to be drawn on graphs with positions dictated by a series of data points:
The plot style of arrows is an alias for arrows_head. Each of these plot styles take four columns of data on two-dimensional plots – , , and – or six columns of data on three-dimensional plots with additional -coordinates. Each data point results in an arrow being drawn from the point to the point . The three plot styles differ in the kinds of arrows that they draw: arrows_head draws an arrow head on each arrow at the point ; arrows_nohead draws simple lines without arrow heads on either end; arrows_twohead draws arrow heads on both ends of each arrow.
Example: A diagram of fluid flow around a vortex
In this example we produce a velocity map of fluid circulating in a vortex. For simplicity, we assume that the fluid in the core of the vortex, at radii
, is undergoing solid body rotation with velocity
, and that the fluid outside this core is behaving as a free vortex with velocity
. First of all, we use a simple python script to generate a data file with the four columns: from math import *for i in range(-19,20,2):for j in range(-19,20,2):x = float(i)/2y = float(j)/2r = sqrt(x**2 + y**2) / 4theta = atan2(y,x)if (r 1.0): v = 1.3*relse : v = 1.3/rvy = v * cos(theta)vx = v * -sin(theta)print "%7.3f %7.3f %7.3f %7.3f"%(x,y,vx,vy)
This data can then be plotted using the following Pyxplot script: set size squareset width 9set nokeyset xlabel ’x’set ylabel ’y’set trange [0:2*pi]plot ’vortex.dat’ u 1:2:($1+$3):($2+$4) w arrows, parametric 4*sin(t):4*cos(t) w lt 2 col black