#!/usr/bin/python3
"""Simple matplotlib+numpy program to plot voltage decay in an RC circuit.

The ``rcParams`` mentioned here is a coincidence; that’s just what
Matplotlib calls its parameters.

"""
import sys
from numpy import linspace, exp
from matplotlib.pyplot import plot, xlabel, ylabel, savefig, rcParams

def plot_rc(tau, outfilename):
    rcParams["pdf.use14corefonts"] = True
    rcParams["ps.useafm"] = True # analogous to use14corefonts for PS/EPS
    t = linspace(0, tau * 6)
    plot(t, exp(-t / tau))
    xlabel("time (seconds)")
    ylabel("fraction of initial $V$")
    savefig(outfilename)

if __name__ == '__main__':
    plot_rc(tau=0.1, outfilename='rc.svg' if len(sys.argv) == 1 else sys.argv[1])