problem based upon coupled oscillatorcoupled oscillator

[gazal sharma]

i have written program for coupled oscillator(nume rical solution)using euler method. but i am not getting the exact graph.can somebdy help me out of it.

K=2
g=9.8
L=8
m=2.0
Tm=10
N=125
h=Tm/float(N)
import matplotlib.pyplot as plt
import numpy as np
import numpy as n1
x1=n1.zeros(N+1)
x2=np.zeros(N+1)
v1=n1.zeros(N+1)
v2=np.zeros(N+1)
t=np.zeros(N+1)
x1[0]=10
x2[0]=0
v1[0]=0
v2[0]=0
i=0
while t[i]<Tm:
    v1[i+1]=(-g/L)*x1[i] - (K/m)*(x1[i]-x2[i])
    v2[i+1]=(-g/L)*x2[i] - (K/m)*(x2[i]-x1[i])
    x1[i+1]=x1[i] + v1[i+1]*h
    x2[i+1]=x2[i] + v2[i+1]*h
    t[i+1]=t[i]+h
    i=i+1
plt.subplot(211)
plt.plot(t,x1)
plt.subplot(212)
plt.plot(t,x2)
plt.show()

[dwblas]

but i am not getting the exact graph

What does this mean. If you are using Python2.x then you should explicitly cast a divide operation to a float, otherwise it is possible to get an integer only as a result.

## -g/float(L)
v1[i+1]=(-g/float(L))*x1[i] - (K/m)*(x1[i]-x2[i]

Also it is possible in the while t[i] statement for "i" to exceed the length of N+1 so you should test for that. Finally, do not use i,l, O, etc as single digit variable names as they look too much like numbers, and to make your code readable by others, take a look at the Python Style Guide, which suggests lower case with underlines for variable names.. An alternative to the while statement (logic only), although there is nothing wrong with the while statement

def check_t(t, Tm, N):
    for ctr in range(N+1):
        if t[ctr] >= Tm:
            return
        ## do the calcs 

    ##raise error as t[ctr] >= Tm was never hit