1. The problem statement, all variables and given/known data I have these two equations from this paper: https://www.scribd.com/doc/299960566/Spiral [Broken] 2. Relevant equations What are the vertical bars next to the drawn red starts supposed to indicate in this context? I'm trying to implement these equations into a program but I'm totally lost. I have no idea what's up with those vertical bars next to the red stars that I drew. Is it supposed to be the terms evaluated at (j+1-rtheta)? If so, then what variable is it even being plugged into (r or theta)? 3. The attempt at a solution Googling and asking my professor.