#!/usr/bin/env pltthon3
# -*- coding: utf-8 -*-
"""
ENGG1811 lecture 7

Example: Simulate the parachutist's speed by formula
"""
# Import 
import para_formula_lib as para
import matplotlib.pyplot as plt 
import numpy as np 

# Problem parameters
mass = 70          # Mass of the parachutist 
time_deploy = 6    # Time at which the parachute is deployed 
air_drag_coeff = 12.5     # Drag coefficient for air
para_drag_coeff = 80      # Drag coefficient for parachute 

# Create a list of regularly spaced time instants
# [0,0.25,0.5,0.75,...,20] 
# 
time_array = np.arange(0,20.1,0.25)

# The function for calculating speed is in a separate file 
# Use for loop to get the speed 
speed_by_formula_array = np.zeros_like(time_array)
for k in range(0,len(time_array)):
    time = time_array[k]
    speed_para = para.parachute(time,mass,air_drag_coeff,time_deploy,para_drag_coeff)
    speed_by_formula_array[k] = speed_para

# Plot the figure 
fig1 = plt.figure() 
plt.plot(time_array,speed_by_formula_array,label = 'Parachute by formula')
plt.legend()
plt.xlabel('time [seconds]')
plt.ylabel('speed [m/s]')
plt.show()
# plt.savefig('para1.png')