Need free program to plot expressions in polar coordinates

1. The problem statement, all variables and given/known data

Need a free program to plot expressions in polar coordinates. For example, I want to plot the equipotentials for an expression in polar coordinates of the potential for a dipole charge, 4q and -q separated by a distance L.





2. Relevant equations

V=kq(4/r₁ - 1/r), where r₁² = r²+ L² - 2rLcosθ.





3. The attempt at a solution

Octave and SciPy/matplotlib are posted online as two (2) good programs.





PS Thank you to Simon for guiding me to a solution for the sheet charge electric field problem I posted.