Exercise W1.1 (four different ways to sum). Recall the summation formula n(n+1) 2 (W1.1.1) EL Write a code that takes a positive integer n e N as input and outputs the sum of the first n natural numbers (strictly positive integers), using: (a) a for loop; (b) a while loop; (c) a recursive code; (d) in Octave/Matlab using an array (also known as vector or finite sequence), the column construct and the built-in function sum. Test your code for n=10, n = 20 and n=100, against the known result" that you are able to compute from (W1.1.1). Do not forget the special case n=0