I have the following program that moves a wave on a string with fixed ends. The program solves the wave equation given a initial condition wave. The initial condition is a triangle wave splitting into two pulses. Here is the code written in Python: Code (Python): from numpy import * from matplotlib.pyplot import * N = 201 # Number of mass points nT = 1200 # Number of time points mi = 0.02 m = [mi]*(N) # mass array of points on string m[-1] = 0.02 m = 0.02 ki = 10. k = [ki]*(N) # Spring constant k[-1] = 0 k = 0 dx = 0.295 kappa = ki*dx my = mi/dx c = sqrt(kappa/my) # velocity print c dt = 0.9*dx/c # Courier x = arange( N )*dx t = arange( N )*dt y = zeros( [N, nT ] ) #Initial condition with t= 0 for i in range(N-1): if (70 <= i <= 99): y[i,0] = (i - 69.)/30 elif (100 <= i <= 128): y[i,0] = ((129 - i)/30.) else: y[i,0] = 0. #Wave equation for j in range(nT-1): for i in range(N-1): if j == 0: y[i,j+1] = 2*y[i,j] - y[i,j] + (dt**2/m[i])*(k[i-1]*y[i+1,j] - 2*k[i-1]*y[i,j] + k[i]*y[i-1,j] ) else: y[i,j+1] = 2*y[i,j] - y[i,j-1] + (dt**2/m[i])*( k[i-1]*y[i+1,j] - 2*k[i-1]*y[i,j] + k[i]*y[i-1,j] ) cla() ylim(-1,1) plot(x,y[:,j-2]) pause(0.001) Here is the plot: I want to make changes to my program so the one triangle wave pulse moves to the right and gets reflected instead of splitting up in two opposite moving pulses. How can I change my initial conditions to make this possible? I want something like this: EDIT:I am not sure if the pictures was correctly added!