[Gretl-users] Check for idempotent matrix in gretl

[Allin Cottrell]

On Fri, 13 Apr 2007, Andreas Karlsson wrote:

> Could you please add a check for idempotency in matrix? So that 
> for a matrix, when one chooses Prpoerties > View the output 
> tells if the matrix is idempotent, just as it now tells if it is 
> e.g. square, symmetric or positive definite.

Yes.  Since we calculate the eigenvalues anyway, I suppose we 
could use them to check for idempotence.  Can anyone remind me how 
that would go (in the general case, allowing for asymmetry)?  
Thanks.

Allin.