#! /usr/bin/env python

# plot1.py
#
# Example python program introducing the use 
# of the matplotlib module.
#
# Paul Eugenio
# PHZ4151C
# Jan 29, 2019


import matplotlib.pyplot as plt
import numpy as np

def cross_section(t):
    """  
    The transverse four-momentum scattering cross section:  t * exp(-t)
    """
    return t*np.exp(-t)



#
# main program
#

# Generate an array of values to plot
x = np.linspace(0,10,101)
y = np.zeros(len(x))
for i in range(len(x)):
    y[i] = cross_section(x[i])


# plotting routines
#
# Figure is saved as a png image and displayed in an X window.

plt.plot(x,y)
plt.savefig("sigma.png")
plt.show()