On the other hand duplication is harder to review. If you have 20 lines of x1 * y[i] + z2 x2 * y[i] + z3 ... or other dense math code, then it tak

On the other hand duplication is harder to review. If you have 20 lines of x1 * y[i] + z2 x2 * y[i] + z3 ... or other dense math code, then it takes a lot of effort to spot any tiny mistake. Duplication vs abstraction is a very context dependent subject, and with many subtleties, one often no best answers.