1DSYEV(1)              LAPACK driver routine (version 3.1)             DSYEV(1)
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NAME

6       DSYEV - all eigenvalues and, optionally, eigenvectors of a real symmet‐
7       ric matrix A
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SYNOPSIS

10       SUBROUTINE DSYEV( JOBZ, UPLO, N, A, LDA, W, WORK, LWORK, INFO )
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12           CHARACTER     JOBZ, UPLO
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14           INTEGER       INFO, LDA, LWORK, N
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16           DOUBLE        PRECISION A( LDA, * ), W( * ), WORK( * )
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PURPOSE

19       DSYEV computes all eigenvalues and, optionally, eigenvectors of a  real
20       symmetric matrix A.
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ARGUMENTS

24       JOBZ    (input) CHARACTER*1
25               = 'N':  Compute eigenvalues only;
26               = 'V':  Compute eigenvalues and eigenvectors.
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28       UPLO    (input) CHARACTER*1
29               = 'U':  Upper triangle of A is stored;
30               = 'L':  Lower triangle of A is stored.
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32       N       (input) INTEGER
33               The order of the matrix A.  N >= 0.
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35       A       (input/output) DOUBLE PRECISION array, dimension (LDA, N)
36               On  entry,  the symmetric matrix A.  If UPLO = 'U', the leading
37               N-by-N upper triangular part of A contains the upper triangular
38               part  of the matrix A.  If UPLO = 'L', the leading N-by-N lower
39               triangular part of A contains the lower triangular part of  the
40               matrix A.  On exit, if JOBZ = 'V', then if INFO = 0, A contains
41               the orthonormal eigenvectors of the matrix A.  If JOBZ  =  'N',
42               then on exit the lower triangle (if UPLO='L') or the upper tri‐
43               angle (if UPLO='U') of A, including the diagonal, is destroyed.
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45       LDA     (input) INTEGER
46               The leading dimension of the array A.  LDA >= max(1,N).
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48       W       (output) DOUBLE PRECISION array, dimension (N)
49               If INFO = 0, the eigenvalues in ascending order.
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51       WORK      (workspace/output)   DOUBLE   PRECISION   array,    dimension
52       (MAX(1,LWORK))
53               On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
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55       LWORK   (input) INTEGER
56               The  length  of  the  array  WORK.  LWORK >= max(1,3*N-1).  For
57               optimal efficiency, LWORK >= (NB+2)*N, where NB is  the  block‐
58               size for DSYTRD returned by ILAENV.
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60               If  LWORK  = -1, then a workspace query is assumed; the routine
61               only calculates the optimal size of  the  WORK  array,  returns
62               this  value  as the first entry of the WORK array, and no error
63               message related to LWORK is issued by XERBLA.
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65       INFO    (output) INTEGER
66               = 0:  successful exit
67               < 0:  if INFO = -i, the i-th argument had an illegal value
68               > 0:  if INFO = i, the algorithm failed  to  converge;  i  off-
69               diagonal  elements  of an intermediate tridiagonal form did not
70               converge to zero.
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74 LAPACK driver routine (version 3.N1o)vember 2006                        DSYEV(1)
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