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

6       DSPEV - computes all the eigenvalues and, optionally, eigenvectors of a
7       real symmetric matrix A in packed storage
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SYNOPSIS

10       SUBROUTINE DSPEV( JOBZ, UPLO, N, AP, W, Z, LDZ, WORK, INFO )
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12           CHARACTER     JOBZ, UPLO
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14           INTEGER       INFO, LDZ, N
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16           DOUBLE        PRECISION AP( * ), W( * ), WORK( * ), Z( LDZ, * )
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PURPOSE

19       DSPEV computes all the eigenvalues and, optionally, eigenvectors  of  a
20       real symmetric matrix A in packed storage.
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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       AP      (input/output) DOUBLE PRECISION array, dimension (N*(N+1)/2)
35               On  entry,  the upper or lower triangle of the symmetric matrix
36               A, packed columnwise in a linear array.  The j-th column  of  A
37               is  stored  in  the  array AP as follows: if UPLO = 'U', AP(i +
38               (j-1)*j/2) =  A(i,j)  for  1<=i<=j;  if  UPLO  =  'L',  AP(i  +
39               (j-1)*(2*n-j)/2)  =  A(i,j)  for j<=i<=n.  On exit, AP is over‐
40               written by values generated during the reduction to tridiagonal
41               form.   If  UPLO = 'U', the diagonal and first superdiagonal of
42               the tridiagonal matrix T overwrite the  corresponding  elements
43               of  A, and if UPLO = 'L', the diagonal and first subdiagonal of
44               T overwrite the corresponding elements of A.
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46       W       (output) DOUBLE PRECISION array, dimension (N)
47               If INFO = 0, the eigenvalues in ascending order.
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49       Z       (output) DOUBLE PRECISION array, dimension (LDZ, N)
50               If JOBZ = 'V', then if INFO = 0,  Z  contains  the  orthonormal
51               eigenvectors of the matrix A, with the i-th column of Z holding
52               the eigenvector associated with W(i).  If JOBZ = 'N', then Z is
53               not referenced.
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55       LDZ     (input) INTEGER
56               The  leading dimension of the array Z.  LDZ >= 1, and if JOBZ =
57               'V', LDZ >= max(1,N).
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59       WORK    (workspace) DOUBLE PRECISION array, dimension (3*N)
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61       INFO    (output) INTEGER
62               = 0:  successful exit.
63               < 0:  if INFO = -i, the i-th argument had an illegal value.
64               > 0:  if INFO = i, the algorithm failed  to  converge;  i  off-
65               diagonal  elements  of an intermediate tridiagonal form did not
66               converge to zero.
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70 LAPACK driver routine (version 3.N2o)vember 2008                        DSPEV(1)
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