Two words, iteration and conditional execution. Most math lacks these features common in programming. With iteration you blend the results at time t with the

Two words, iteration and conditional execution. Most math lacks these features common in programming. With iteration you blend the results at time t with the results at time t+1. Because of conditionals (if statements), a programming mistake at time t may not become evident till some much later step in the iteration, because the path through the logic is not guaranteed to be consistent. Typically the data of all intervening steps has been lost by the time you encounter the error.