Re: [Gretl-users] diagcat

On Fri, 28 Sep 2012, Sven Schreiber wrote: > Good morning, > > I just noticed the new (?) function diagcat() with the following help > text: > > "Returns the direct sum of A and B, that is a block-diagonal matrix > holding A in its north-west corner and B in its south-east corner. " > > Why would that be a _sum_? Because that's its name :) http://en.wikipedia.org/wiki/Matrix_addition#Direct_sum Intuitively, you can think of this operator as a sum if you view matrices as the space spanned by their columns. The direct sum of two matrices results in a space which is equal to the two original spaces "put together", so to speak.

> Also, what happens if A and B are not square? (I know, I could just try > that out, but too lazy, and that wouldn't necessarily answer what's > intended as a result.) Nothing spectacular. You just have non-square zero blocks in the north-east and south-west corners of the result.