![Filling an Upper Triangular Matrix from a Vector](https://blogs.sas.com/content/iml/files/2017/02/AdvancedAnalytics-3.png)
Filling an Upper Triangular Matrix from a Vector
The R You Ready blog posed an interesting problem. Essentially, you have a vector that contains n(n+1)/2 elements, and you want to pack those elements into the upper left triangular portion of a matrix. For example, if your data are proc iml; /** vector v is given: ncol(v) = n(n+1)/2 for