Simulation of standing waves

from pylab import*
a=2.0
lam=1.0
v=1.0
tmax=10
xmax=3
dt=0.05
x=linspace(0,xmax,1000)
t=0
while t<=tmax:
    y=a*(sin(2*pi*(x-v*t)/lam)+sin(2*pi*(x+v*t)/lam))
    plot(x,y,'b')
    t=t+dt

show()