A Note on the vec Operator Applied to Unbalanced Block Structured Matrices
The vec operator transforms a matrix to a column vector by stacking each column on top of the next. It is useful to write the vec of a block structured matrix in terms of the vec operator applied to each of its component blocks. We derive a simple formula for doing so, which applies regardless of whether the blocks are of the same or of different sizes.
J. Appl. Math.