.TH SSPEV 1 "November 2006" " LAPACK driver routine (version 3.1) " " LAPACK driver routine (version 3.1) " .SH NAME SSPEV - all the eigenvalues and, optionally, eigenvectors of a real symmetric matrix A in packed storage .SH SYNOPSIS .TP 18 SUBROUTINE SSPEV( JOBZ, UPLO, N, AP, W, Z, LDZ, WORK, INFO ) .TP 18 .ti +4 CHARACTER JOBZ, UPLO .TP 18 .ti +4 INTEGER INFO, LDZ, N .TP 18 .ti +4 REAL AP( * ), W( * ), WORK( * ), Z( LDZ, * ) .SH PURPOSE SSPEV computes all the eigenvalues and, optionally, eigenvectors of a real symmetric matrix A in packed storage. .SH ARGUMENTS .TP 8 JOBZ (input) CHARACTER*1 = \(aqN\(aq: Compute eigenvalues only; .br = \(aqV\(aq: Compute eigenvalues and eigenvectors. .TP 8 UPLO (input) CHARACTER*1 .br = \(aqU\(aq: Upper triangle of A is stored; .br = \(aqL\(aq: Lower triangle of A is stored. .TP 8 N (input) INTEGER The order of the matrix A. N >= 0. .TP 8 AP (input/output) REAL array, dimension (N*(N+1)/2) On entry, the upper or lower triangle of the symmetric matrix A, packed columnwise in a linear array. The j-th column of A is stored in the array AP as follows: if UPLO = \(aqU\(aq, AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; if UPLO = \(aqL\(aq, AP(i + (j-1)*(2*n-j)/2) = A(i,j) for j<=i<=n. On exit, AP is overwritten by values generated during the reduction to tridiagonal form. If UPLO = \(aqU\(aq, the diagonal and first superdiagonal of the tridiagonal matrix T overwrite the corresponding elements of A, and if UPLO = \(aqL\(aq, the diagonal and first subdiagonal of T overwrite the corresponding elements of A. .TP 8 W (output) REAL array, dimension (N) If INFO = 0, the eigenvalues in ascending order. .TP 8 Z (output) REAL array, dimension (LDZ, N) If JOBZ = \(aqV\(aq, then if INFO = 0, Z contains the orthonormal eigenvectors of the matrix A, with the i-th column of Z holding the eigenvector associated with W(i). If JOBZ = \(aqN\(aq, then Z is not referenced. .TP 8 LDZ (input) INTEGER The leading dimension of the array Z. LDZ >= 1, and if JOBZ = \(aqV\(aq, LDZ >= max(1,N). .TP 8 WORK (workspace) REAL array, dimension (3*N) .TP 8 INFO (output) INTEGER = 0: successful exit. .br < 0: if INFO = -i, the i-th argument had an illegal value. .br > 0: if INFO = i, the algorithm failed to converge; i off-diagonal elements of an intermediate tridiagonal form did not converge to zero.