SLOG #5: Recursion

   Recursion, a method used to define an object in terms of itself. It is done this way so you can achieve a certain objective once you use recursion for several times. For instance, we can find factorials such 5! recursively because
n! = n x (n - 1) x (n-2) x … x 2 x 1 = (n)[(n - 1)!]
where n is an integer and n >= 1. Since programming language generally support recursion, this means functions can be used to call themselves to solve problems where recursion is involved. Most of the times, coding recursion will require precision, since the answers to the problem depends on the solution to their smaller instance calls. 

   If we were to code factorials by means of recursion in python, we can return the product of the number multiply by the recursive call using the number that is 1 less than the current number. If the current number is 0 or 1, return 1. This means we can code it as the following:

def factorial(n) :

               if n == 0 or n == 1:

                              return 1

               elif n > 1:

                              return n * factorial(n - 1)   

   It is also possible to do recursion such as factorial using loops, but not all recursive problems can be solved without applying recursive calls.  For example, to the sum of all the numbers in a list that contains lists of numbers and numbers. For such recursive data structures, recursive calls can be used when the recursion depth is either unknown or too large to code without recursion.

Often, it is possible such that our coded recursive function may receive errors such as 

RuntimeError: maximum recursion depth exceeded

when the default maximum recursion call limit is reached once a recursion call is recursively called for a certain amount. The error can be fixed by either change the default recursion call limit or create a more efficient recursive function that requires less calls needed. If the object we performed recursion calls on have an infinite recursion depth, recursion will not work if the Runtime Error was not caught.  

   From the lectures in the recent weeks, we learnt about Tree structures, which have a recursive data structure built in such a way that each Tree object either links to sub Tree objects or nothing. It can be used to represent to group data collectively in groups and subgroups. 

   From the past weeks, we have done countless samples regarding recursion in class, and was test on recursion in the recent midterm. It is import for csc students such as myself to know how to use recursion and write code of it.