Arguments

A

(input/output) REAL or COMPLEX square array, shape $(:,:)$.
On entry, the matrix $A$.
On exit, the Schur form $T$.

w

(output) REAL or COMPLEX array, shape $(:)$ with $size({\it w}) = size({\bf A},1)$.
The computed eigenvalues in the order in which they appear on the diagonal of the Schur form $T$.
${\it w(:)}$ ::= WR(:), WI(:) $\mid$ W(:),
where
WR(:), WI(:) are of REAL type (for the real and imaginary parts) and W(:) is of COMPLEX type.
Note: If $A$ is real, then a complex-conjugate pair appear consecutively, with the eigenvalue having the positive imaginary part appearing first.

VS

Optional (output) REAL or COMPLEX square array, shape $(:,:)$ with $size$(VS,1) $= size$(A,1).
The matrix $Z$ of Schur vectors.

SELECT

Optional (input) LOGICAL FUNCTION.

LOGICAL FUNCTION SELECT( w$_j$ )
type(wp), INTENT(IN) :: w$_j$
where
type ::= REAL $\mid$ COMPLEX
wp ::= KIND(1.0) $\mid$ KIND(1.0D0)
w$_j$ ::= WR$_j$, WI$_j$ $\mid$ W$_j$

Note: Select must be present if SDIM is desired.

SDIM

Optional (output) INTEGER.
The number of eigenvalues (after sorting) for which SELECT $=$ .TRUE. (If $A$ is real, complex conjugate pairs for which SELECT $=$ .TRUE. for either eigenvalue count as 2).

INFO

Optional (output) INTEGER.


If ${\bf INFO}$ is not present and an error occurs, then the program is terminated with an error message.

References: [1] and [17,9,20].