Interference of 1D waves

The code

This is the SAGE code that produces the images: h = 0.5
off = -3.7
def ir_ha(x):
    if x<0: x = -x
    if x>2: return 0
    if x>1: return (2-x)^3/4
    return (3*x^3-6*x^2+4)/4

def f1(x):
    x /= h
    x -= off
    return ir_ha(x)*sin(x^2+4*x-0.7)

def f2(x):
    x /= h
    x += off
    return ir_ha(x)*cos(2.0*x)

def u(x,t):
    return f1(x-t)+f2(x+t)
   

k = 0
for t in srange(0,4.6,0.8):
    def w0(x):
        return u(x,t)
    P = plot( w0, x,-4, 4, thickness=4, ymin=-1, ymax=1.1)
    if k==0:
        P += text('$f_1$',(off+2.3,-0.7), fontsize=30 )
        P += text('$f_2$',(-off-1.8,-0.7), fontsize=30 )
    P += text('$t=$'+str(k),(-4,0.7), fontsize=30 )
    P.fontsize(25)
    P.set_aspect_ratio(1)
    P.axes(False)
    P.save('../images/1dwav'+str(k)+'.eps')
    k += 1