Arguments

AP

(input/output) REAL or COMPLEX array, shape $(:)$ with $size({\bf AP}) = n(n+1)/2$, where $n$ is the order of $A$.
On entry, the upper or lower triangle of matrix $A$ in packed storage. The elements are stored columnwise as follows:

$$\begin{array}{c\vert c\vert c} A_{i,j} & i,j & {\bf UPLO} ... ... \leq i \leq n \end{array} & \mbox{ 'L'} \\ \hline \end{array}$$

On exit, ${\bf AP}$ is overwritten by values generated during the reduction of $A$ to a tridiagonal matrix $T$. If ${\bf UPLO} =$ 'U', the diagonal and first superdiagonal of T overwrite the corresponding diagonals of $A$. If ${\bf UPLO} =$ 'L', the diagonal and first subdiagonal of T overwrite the corresponding diagonals of $A$.

W

(output) REAL array, shape $(:)$ with $size({\bf W}) = n$.
The eigenvalues in ascending order.

UPLO

Optional (input) CHARACTER(LEN=1).


Default value: 'U'.

Z

Optional (output) REAL or COMPLEX square array, shape $(:,:)$ with $size({\bf Z},1) = n$.
The columns of ${\bf Z}$ contain the orthonormal eigenvectors of $A$ in the order of the eigenvalues.

INFO

Optional (output) INTEGER.


If INFO is not present and an error occurs, then the program is terminated with an error message.

References: [1] and [17,9,20].