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.