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

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

10       SUBROUTINE SSYEV( 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           REAL          A( LDA, * ), W( * ), WORK( * )
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PURPOSE

19       SSYEV 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) REAL 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) REAL array, dimension (N)
49               If INFO = 0, the eigenvalues in ascending order.
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51       WORK    (workspace/output) REAL array, dimension (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 SSYTRD returned by ILAENV.
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59               If LWORK = -1, then a workspace query is assumed;  the  routine
60               only  calculates  the  optimal  size of the WORK array, returns
61               this value as the first entry of the WORK array, and  no  error
62               message related to LWORK is issued by XERBLA.
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64       INFO    (output) INTEGER
65               = 0:  successful exit
66               < 0:  if INFO = -i, the i-th argument had an illegal value
67               >  0:   if  INFO  = i, the algorithm failed to converge; i off-
68               diagonal elements of an intermediate tridiagonal form  did  not
69               converge to zero.
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73 LAPACK driver routine (version 3.N1o)vember 2006                        SSYEV(1)
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