ssyt01_3.f

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*> \brief \b SSYT01_3
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*  Definition:
*  ===========
*
*       SUBROUTINE SSYT01_3( UPLO, N, A, LDA, AFAC, LDAFAC, E, IPIV, C,
*                            LDC, RWORK, RESID )
*
*       .. Scalar Arguments ..
*       CHARACTER          UPLO
*       INTEGER            LDA, LDAFAC, LDC, N
*       DOUBLE PRECISION   RESID
*       ..
*       .. Array Arguments ..
*       INTEGER            IPIV( * )
*       DOUBLE PRECISION   A( LDA, * ), AFAC( LDAFAC, * ), C( LDC, * ),
*      $                   E( * ), RWORK( * )
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> SSYT01_3 reconstructs a symmetric indefinite matrix A from its
*> block L*D*L' or U*D*U' factorization computed by SSYTRF_RK
*> (or SSYTRF_BK) and computes the residual
*>    norm( C - A ) / ( N * norm(A) * EPS ),
*> where C is the reconstructed matrix and EPS is the machine epsilon.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] UPLO
*> \verbatim
*>          UPLO is CHARACTER*1
*>          Specifies whether the upper or lower triangular part of the
*>          symmetric matrix A is stored:
*>          = 'U':  Upper triangular
*>          = 'L':  Lower triangular
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>          The number of rows and columns of the matrix A.  N >= 0.
*> \endverbatim
*>
*> \param[in] A
*> \verbatim
*>          A is DOUBLE PRECISION array, dimension (LDA,N)
*>          The original symmetric matrix A.
*> \endverbatim
*>
*> \param[in] LDA
*> \verbatim
*>          LDA is INTEGER
*>          The leading dimension of the array A.  LDA >= max(1,N)
*> \endverbatim
*>
*> \param[in] AFAC
*> \verbatim
*>          AFAC is DOUBLE PRECISION array, dimension (LDAFAC,N)
*>          Diagonal of the block diagonal matrix D and factors U or L
*>          as computed by SSYTRF_RK and SSYTRF_BK:
*>            a) ONLY diagonal elements of the symmetric block diagonal
*>               matrix D on the diagonal of A, i.e. D(k,k) = A(k,k);
*>               (superdiagonal (or subdiagonal) elements of D
*>                should be provided on entry in array E), and
*>            b) If UPLO = 'U': factor U in the superdiagonal part of A.
*>               If UPLO = 'L': factor L in the subdiagonal part of A.
*> \endverbatim
*>
*> \param[in] LDAFAC
*> \verbatim
*>          LDAFAC is INTEGER
*>          The leading dimension of the array AFAC.
*>          LDAFAC >= max(1,N).
*> \endverbatim
*>
*> \param[in] E
*> \verbatim
*>          E is DOUBLE PRECISION array, dimension (N)
*>          On entry, contains the superdiagonal (or subdiagonal)
*>          elements of the symmetric block diagonal matrix D
*>          with 1-by-1 or 2-by-2 diagonal blocks, where
*>          If UPLO = 'U': E(i) = D(i-1,i),i=2:N, E(1) not referenced;
*>          If UPLO = 'L': E(i) = D(i+1,i),i=1:N-1, E(N) not referenced.
*> \endverbatim
*>
*> \param[in] IPIV
*> \verbatim
*>          IPIV is INTEGER array, dimension (N)
*>          The pivot indices from SSYTRF_RK (or SSYTRF_BK).
*> \endverbatim
*>
*> \param[out] C
*> \verbatim
*>          C is DOUBLE PRECISION array, dimension (LDC,N)
*> \endverbatim
*>
*> \param[in] LDC
*> \verbatim
*>          LDC is INTEGER
*>          The leading dimension of the array C.  LDC >= max(1,N).
*> \endverbatim
*>
*> \param[out] RWORK
*> \verbatim
*>          RWORK is DOUBLE PRECISION array, dimension (N)
*> \endverbatim
*>
*> \param[out] RESID
*> \verbatim
*>          RESID is DOUBLE PRECISION
*>          If UPLO = 'L', norm(L*D*L' - A) / ( N * norm(A) * EPS )
*>          If UPLO = 'U', norm(U*D*U' - A) / ( N * norm(A) * EPS )
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup single_lin
*
*  =====================================================================
      SUBROUTINE ssyt01_3( UPLO, N, A, LDA, AFAC, LDAFAC, E, IPIV, C,
     $                     LDC, RWORK, RESID )
*
*  -- LAPACK test routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      CHARACTER          UPLO
      INTEGER            LDA, LDAFAC, LDC, N
      REAL               RESID
*     ..
*     .. Array Arguments ..
      INTEGER            IPIV( * )
      REAL               A( LDA, * ), AFAC( LDAFAC, * ), C( LDC, * ),
     $                   e( * ), rwork( * )
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      REAL               ZERO, ONE
      parameter( zero = 0.0e+0, one = 1.0e+0 )
*     ..
*     .. Local Scalars ..
      INTEGER            I, INFO, J
      REAL               ANORM, EPS
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      REAL               SLAMCH, SLANSY
      EXTERNAL           lsame, slamch, slansy
*     ..
*     .. External Subroutines ..
      EXTERNAL           slaset, slavsy_rook, ssyconvf_rook
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          real
*     ..
*     .. Executable Statements ..
*
*     Quick exit if N = 0.
*
      IF( n.LE.0 ) THEN
         resid = zero
         RETURN
      END IF
*
*     a) Revert to multipliers of L
*
      CALL ssyconvf_rook( uplo, 'R', n, afac, ldafac, e, ipiv, info )
*
*     1) Determine EPS and the norm of A.
*
      eps = slamch( 'Epsilon' )
      anorm = slansy( '1', uplo, n, a, lda, rwork )
*
*     2) Initialize C to the identity matrix.
*
      CALL slaset( 'Full', n, n, zero, one, c, ldc )
*
*     3) Call SLAVSY_ROOK to form the product D * U' (or D * L' ).
*
      CALL slavsy_rook( uplo, 'Transpose', 'Non-unit', n, n, afac,
     $                  ldafac, ipiv, c, ldc, info )
*
*     4) Call SLAVSY_ROOK again to multiply by U (or L ).
*
      CALL slavsy_rook( uplo, 'No transpose', 'Unit', n, n, afac,
     $                  ldafac, ipiv, c, ldc, info )
*
*     5) Compute the difference  C - A.
*
      IF( lsame( uplo, 'U' ) ) THEN
         DO j = 1, n
            DO i = 1, j
               c( i, j ) = c( i, j ) - a( i, j )
            END DO
         END DO
      ELSE
         DO j = 1, n
            DO i = j, n
               c( i, j ) = c( i, j ) - a( i, j )
            END DO
         END DO
      END IF
*
*     6) Compute norm( C - A ) / ( N * norm(A) * EPS )
*
      resid = slansy( '1', uplo, n, c, ldc, rwork )
*
      IF( anorm.LE.zero ) THEN
         IF( resid.NE.zero )
     $      resid = one / eps
      ELSE
         resid = ( ( resid / real( n ) ) / anorm ) / eps
      END IF
 
*
*     b) Convert to factor of L (or U)
*
      CALL ssyconvf_rook( uplo, 'C', n, afac, ldafac, e, ipiv, info )
*
      RETURN
*
*     End of SSYT01_3
*
      END