example_plot.py

import matplotlib.pyplot as plt
import numpy as np

trip_distance = 6.0 # km
trip_duration = 12.0 # minutes
trip_avg_speed = 30.0 # km/h

# trip duration in minutes
def duration(distance, speed):
    return distance * 1/speed * 60.0

real_duration = duration(trip_distance, trip_avg_speed)

speeds = np.linspace(5, 50)
duration = np.vectorize(lambda speed: duration(trip_distance, speed))(speeds)
error = 12 - duration

fig, ax = plt.subplots()
ax.grid(True, which='both')

ax.plot(speeds, duration, label='Trip duration wrt speed')
ax.plot(speeds, error, label='Error wrt to speed param')
ax.scatter([trip_avg_speed], [0], label='Error for real average speed')

plt.xlabel('average speed')
plt.legend()
plt.show()