Fix plot script and get rid of pandas dependency

import matplotlib as mpl

mpl.use('Agg')

import matplotlib.pyplot as plt

import pandas

import numpy as np

def main():

   parser = argparse.ArgumentParser(description="Plot the solver residuals for the CTF solution")

   parser.add_argument('residual_file', type=str, help="The .ctf.residuals.csv file produced by CTF")

   args = parser.parse_args()

   csv = pandas.read_csv(args.residual_file, comment='#')

   csv = np.loadtxt(args.residual_file, delimiter=',', skiprows=4, comments='#')

   timestep = list(range(len(csv['dav_li'].tolist())))

   timestep = list(range(csv.shape[0]))

   fig, ax = plt.subplots()

   plt.title('Vapor and droplet void residuals')

   ax.grid()

   ax.set_xlabel("Timestep")

   ax.set_ylabel("Residual [-]")

   ax.plot(timestep, csv['dav_li'].tolist(), label='av l-inf')

   ax.plot(timestep, csv['dav_l2'].tolist(), label='av l2')

   ax.plot(timestep, csv['dae_li'].tolist(), label='ae l-inf')

   ax.plot(timestep, csv['dae_l2'].tolist(), label='ae l2')

   ax.plot(timestep, csv[:, 0], label='av l-inf')

   ax.plot(timestep, csv[:, 3], label='av l2')

   ax.plot(timestep, csv[:, 4].tolist(), label='ae l-inf')

   ax.plot(timestep, csv[:, 7].tolist(), label='ae l2')

   ax.legend()

   plt.savefig('void.png')

   plt.close(fig)

   plt.title('Pressure residuals')

   ax.grid()

   ax.set_xlabel("Timestep")

   ax.set_ylabel("Residual [psi]")

   ax.plot(timestep, csv['dp_li'].tolist(), label='p l-inf')

   ax.plot(timestep, csv['dp_l2'].tolist(), label='p l2')

   ax.plot(timestep, csv['dng_li'].tolist(), label='gas l-inf')

   ax.plot(timestep, csv['dng_l2'].tolist(), label='gas l2')

   ax.set_ylabel("Residual [bar]")

   ax.plot(timestep, csv[:, 16], label='p l-inf')

   ax.plot(timestep, csv[:, 19], label='p l2')

   ax.plot(timestep, csv[:, 20], label='gas l-inf')

   ax.plot(timestep, csv[:, 23], label='gas l2')

   ax.legend()

   plt.savefig('pressure.png')

   plt.close(fig)

   plt.title('Enthalpy residuals')

   ax.grid()

   ax.set_xlabel("Timestep")

   ax.set_ylabel("Residual [BTU/lbm]")

   ax.plot(timestep, csv['davhv_li'].tolist(), label='av*hv l-inf')

   ax.plot(timestep, csv['davhv_l2'].tolist(), label='av*hv l2')

   ax.plot(timestep, csv['daelhl_li'].tolist(), label='(1-av)*hl l-inf')

   ax.plot(timestep, csv['daelhl_l2'].tolist(), label='(1-av)*hl l2')

   ax.set_ylabel("Residual [kJ/kg]")

   ax.plot(timestep, csv[:, 8], label='av*hv l-inf')

   ax.plot(timestep, csv[:, 11], label='av*hv l2')

   ax.plot(timestep, csv[:, 12], label='(1-av)*hl l-inf')

   ax.plot(timestep, csv[:, 15].tolist(), label='(1-av)*hl l2')

   ax.legend()

   plt.savefig('enthalpy.png')

   plt.close(fig)