Exercise W1.1 (four different ways to sum). Recall the summation formula ;= n(n+1) 2 = 2 (W1.1.1) i=1 Write a code that takes a positive integer ne 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