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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{displaymath}
\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}\end{displaymath}

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).

\begin{optionarg}
\item[{$=$\ 'U':}] Upper triangle of $A$\ is stored;
\item[{$=$\ 'L':}] Lower triangle of $A$\ is stored.
\end{optionarg}
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.

\begin{infoarg}
\item[{$=$\ 0:}] successful exit.
\item[{$<$\ 0:}] if {\bf INF...
...ts of an intermediate tridiagonal
form did not converge to zero.
\end{infoarg}
If INFO is not present and an error occurs, then the program is terminated with an error message.
References: [1] and [17,9,20].
next up previous contents index
Next: Examples Up: Standard Symmetric Eigenvalue Problems Previous: Purpose   Contents   Index
Susan Blackford 2001-08-19