"""
Exponential growth model with data saving
"""

import numpy as np
steps = 10
t = np.zeros(steps+1)
N = np.zeros(steps+1)
r = 0.5
t[0] = 0
N[0] = 2
for i in range( steps ):
    N[i+1] = N[i] + r * N[i]
    t[i+1] = t[i] + 1
    
for i in range( steps+1 ):
    print( f"At time {t[i]}, N is {N[i]:6.4f}" )
    
# One way to save the data
f = open( "ExpGrowth.txt", "w" )
for i in range( steps+1 ):
    print( f"{t[i]:4.1f} \t {N[i]:7.4f}", file=f )
f.close()

# An alternate way to save the data
output = np.column_stack( (t,N) )
np.savetxt( "ExpGrowth2.txt", output, fmt="%6.4f")