1DSYEV(1)              LAPACK driver routine (version 3.2)             DSYEV(1)
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NAME

6       DSYEV  -  computes  all  eigenvalues and, optionally, eigenvectors of a
7       real symmetric 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

23       JOBZ    (input) CHARACTER*1
24               = 'N':  Compute eigenvalues only;
25               = 'V':  Compute eigenvalues and eigenvectors.
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27       UPLO    (input) CHARACTER*1
28               = 'U':  Upper triangle of A is stored;
29               = 'L':  Lower triangle of A is stored.
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31       N       (input) INTEGER
32               The order of the matrix A.  N >= 0.
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34       A       (input/output) DOUBLE PRECISION array, dimension (LDA, N)
35               On  entry,  the symmetric matrix A.  If UPLO = 'U', the leading
36               N-by-N upper triangular part of A contains the upper triangular
37               part  of the matrix A.  If UPLO = 'L', the leading N-by-N lower
38               triangular part of A contains the lower triangular part of  the
39               matrix A.  On exit, if JOBZ = 'V', then if INFO = 0, A contains
40               the orthonormal eigenvectors of the matrix A.  If JOBZ  =  'N',
41               then on exit the lower triangle (if UPLO='L') or the upper tri‐
42               angle (if UPLO='U') of A, including the diagonal, is destroyed.
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44       LDA     (input) INTEGER
45               The leading dimension of the array A.  LDA >= max(1,N).
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47       W       (output) DOUBLE PRECISION array, dimension (N)
48               If INFO = 0, the eigenvalues in ascending order.
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50       WORK      (workspace/output)   DOUBLE   PRECISION   array,    dimension
51       (MAX(1,LWORK))
52               On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
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54       LWORK   (input) INTEGER
55               The  length  of  the  array  WORK.  LWORK >= max(1,3*N-1).  For
56               optimal efficiency, LWORK >= (NB+2)*N, where NB is  the  block‐
57               size  for  DSYTRD  returned  by  ILAENV.  If LWORK = -1, then a
58               workspace query is assumed; the  routine  only  calculates  the
59               optimal size of the WORK array, returns this value as the first
60               entry of the WORK array, and no error message related to  LWORK
61               is issued by XERBLA.
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63       INFO    (output) INTEGER
64               = 0:  successful exit
65               < 0:  if INFO = -i, the i-th argument had an illegal value
66               >  0:   if  INFO  = i, the algorithm failed to converge; i off-
67               diagonal elements of an intermediate tridiagonal form  did  not
68               converge to zero.
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72 LAPACK driver routine (version 3.N2o)vember 2008                        DSYEV(1)
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