# FreeBSD Manual Pages

```PDLAED0(l)			       )			    PDLAED0(l)

NAME
PDLAED0	-  compute all eigenvalues and corresponding eigenvectors of a
symmetric tridiagonal matrix using the divide and conquer method

SYNOPSIS
SUBROUTINE PDLAED0( N, D, E, Q, IQ, JQ, DESCQ, WORK, IWORK, INFO	)

INTEGER	   INFO, IQ, JQ, N

INTEGER	   DESCQ( * ), IWORK( *	)

DOUBLE	   PRECISION D(	* ), E(	* ), Q(	* ), WORK( * )

PURPOSE
PDLAED0 computes	all eigenvalues	and corresponding  eigenvectors	 of  a
symmetric tridiagonal matrix using the divide and conquer method.

ARGUMENTS
N       (global input) INTEGER
The order of the	tridiagonal matrix T.  N >= 0.

D       (global input/output) DOUBLE PRECISION array, dimension (N)
On  entry, the diagonal elements	of the tridiagonal matrix.  On
exit, if	INFO = 0, the eigenvalues in descending	order.

E       (global input/output) DOUBLE PRECISION array, dimension (N-1)
On entry, the subdiagonal elements of the  tridiagonal  matrix.
On exit,	E has been destroyed.

Q       (local output) DOUBLE PRECISION array,
global dimension	(N, N),	local dimension	( LLD_Q, LOCc(JQ+N-1))
Q  contains  the	 orthonormal  eigenvectors  of	the  symmetric
tridiagonal  matrix.   On output, Q is distributed across the P
processes in block cyclic format.

IQ      (global input) INTEGER
Q's global row index, which points to the beginning of the sub-
matrix which is to be operated on.

JQ      (global input) INTEGER
Q's  global  column index, which	points to the beginning	of the
submatrix which is to be	operated on.

DESCQ   (global and local input)	INTEGER	array of dimension DLEN_.
The array descriptor for	the distributed	matrix Z.

WORK    (local workspace	) DOUBLE PRECISION array, dimension (LWORK)
LWORK = 6*N + 2*NP*NQ, with NP =	NUMROC(	N, MB_Q, MYROW,	IQROW,
NPROW ) NQ = NUMROC( N, NB_Q, MYCOL, IQCOL, NPCOL ) IQROW = IN-
DXG2P( IQ, NB_Q,	MYROW, RSRC_Q, NPROW ) IQCOL  =	 INDXG2P(  JQ,
MB_Q, MYCOL, CSRC_Q, NPCOL )

IWORK   (local workspace/output)	INTEGER	array, dimension (LIWORK)
LIWORK =	2 + 7*N	+ 8*NPCOL

INFO    (global output) INTEGER
= 0:  successful	exit
<  0:   If the i-th argument is an array	and the	j-entry	had an
illegal value, then INFO	= -(i*100+j), if the i-th argument  is
a  scalar  and had an illegal value, then INFO =	-i.  > 0:  The
algorithm failed	to compute the INFO/(N+1) th eigenvalue	 while
working	on  the	 submatrix  lying  in  global rows and columns
mod(INFO,N+1).

ScaLAPACK version 1.7		13 August 2001			    PDLAED0(l)
```

NAME | SYNOPSIS | PURPOSE | ARGUMENTS

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