

 
PSLAED0  compute all eigenvalues and corresponding eigenvectors of a symmetric
tridiagonal matrix using the divide and conquer method
 SUBROUTINE PSLAED0(
 N, D, E, Q, IQ, JQ, DESCQ, WORK, IWORK, INFO )
INTEGER INFO, IQ, JQ, N INTEGER DESCQ( * ), IWORK( * ) REAL D( * ), E( * ), Q( *
), WORK( * )
PSLAED0 computes all eigenvalues and corresponding eigenvectors of a symmetric
tridiagonal matrix using the divide and conquer method.
 N (global input) INTEGER
 The order of the tridiagonal matrix T. N >= 0.
 D (global input/output) REAL 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) REAL array, dimension (N1)
 On entry, the subdiagonal elements of the tridiagonal matrix. On exit, E
has been destroyed.
 Q (local output) REAL array,
 global dimension (N, N), local dimension ( LLD_Q, LOCc(JQ+N1)) 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 submatrix 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 ) REAL 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 = INDXG2P( 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 ith argument is an array and the jentry had an illegal
value, then INFO = (i*100+j), if the ith 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).
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