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# Manual Reference Pages  -  PDLAED0 (l)

### NAME

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

Synopsis
Purpose
Arguments

### 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 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 ) 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 = 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 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).
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 ScaLAPACK version 1.7 PDLAED0 (l) 13 August 2001

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