logistic.py
#!/usr/bin/python
#-------------------------------------------------------
#
# logistic.py - A simple differential equation model
# of a logistic equation.
# Translated to Python from the TrueBasic program
# in "Calculus in Context" by Callahan and Hoffman.
#
# Translated by Barry Tolnas, tolnasb@evergreen.edu
#------------------------------------------------------
from visual.graph import *
tinitial = 0
tfinal = 75
graph = gdisplay()
for numberofsteps in range(1,11):
t = tinitial
y = 100
deltat = (tfinal - tinitial)/numberofsteps
ycurve = gcurve(color=(numberofsteps/10.0,0,1-numberofsteps/10.0))
#print initial values at time 0
print t, y
ycurve.plot(pos=(t,y))
for k in range(numberofsteps):
#compute rate of change
yprime = .1*y*(1-y/1000)
#compute amount of change (deltas)
deltay = yprime*deltat
#update variables
t = t + deltat
y = y + deltay
#print out the results for this timestep
print t,y
ycurve.plot(pos=(t,y))
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