product-of-the-main-diagonal-of-a-square-matrix

Product of the main diagonal of a square matrix

Given a list of rows of a square matrix, find the product of the main diagonal.

Examples:

  [[1, 0], [0, 1]] should return 1
  [[1, 2, 3], [4, 5, 6], [7, 8, 9]] should return 45

http://en.wikipedia.org/wiki/Main_diagonal