Stacking Vectors and Matrixes

Description

Stacks either a lower triangle matrix or a matrix.

Usage

vec(x)
vech(x)

Arguments

Details

The function vec implements the operator that stacks a matrix as a column vector, to be more precise in a matrix with one column. vec(X) = (X11, X21, ..., XN1, X12, X22, ..., XNN).

The function vech implements the operator that stacks the lower triangle of a NxN matrix as an N(N+1)/2x1 vector: vech(X) =(X11, X21, X22, X31, ..., XNN), to be more precise in a matrix with one row.

Examples

## Create Pascal Matrix:
   P = pascal(3)
   
## Stack a matrix
   vec(P) 
   
## Stack the lower triangle
   vech(P)