A Note on the vec Operator Applied to Unbalanced Block-Structured Matrices

الملخص EN

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.