1. The problem statement, all variables and given/known data This one 2. Relevant equations ALL of them! 3. The attempt at a solution This is a beginning to a long physics problems, but the idea is to describe the potential above as something periodical. For example: This potential can be written as ##V(x)=\sum _n [H(x-na)-H(x-na-\frac a 3)]## if ##H(x)## is Heaviside function. Ok, back to original problem. I have no idea how to do it. I tried to work with periodic absolute values, but, it doesn't work out the way it should. Any ideas?