#!/usr/bin/env python
#integrates the lorenz equations
#usage: lorenz.py
#with no options specified, the defaults makes a nice attractor
import sys, getopt
tstop=100
dt=.02
a=5.
b=15.
c=1.
(options,arguements)=getopt.getopt(sys.argv[1:],'a:b:c:',["tstop=","dt="])
for op,ar in options:
    if op=="--tstop": tstop=eval(ar)
    if op=="--dt": dt=eval(ar)
    if op=="-a": a=eval(ar)
    if op=="-b": b=eval(ar)
    if op=="-c": c=eval(ar)
pfile=open('lorenz.dat','w')
pfile.write("#Lorenz attractor written by lorenz.py \n")
pfile.write("#a=%6.2f  b=%6.2f   c=%6.2f \n" % (a,b,c))
t=0
x=1
y=0
z=0
while t<tstop:
    t=t+dt
    dxdt=a*y-a*x
    dydt=b*x-y-z*x
    dzdt=x*y-c*z
    x=x+dxdt*dt
    y=y+dydt*dt
    z=z+dzdt*dt
    pfile.write("%f %f %f %f\n" % (t,x,y,z))
pfile.close()
print "file lorenz.dat was written"