![Filling the lower and upper triangular portions of a matrix](https://blogs.sas.com/content/iml/files/2012/09/t_lowertriang.png)
If you use a word three times, it's yours. -Unknown When I was a child, my mother used to encourage me to increase my vocabulary by saying, "If you use a word three times, it's yours for life." I believe that the same saying holds for programming techniques: Use a