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SUBROUTINE DSYT01( UPLO, N, A, LDA, AFAC, LDAFAC, IPIV, C, LDC,
$ RWORK, RESID )
*
* -- LAPACK test routine (version 3.0) --
* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
* Courant Institute, Argonne National Lab, and Rice University
* September 30, 1994
*
* .. Scalar Arguments ..
CHARACTER UPLO
INTEGER LDA, LDAFAC, LDC, N
DOUBLE PRECISION RESID
* ..
* .. Array Arguments ..
INTEGER IPIV( * )
DOUBLE PRECISION A( LDA, * ), AFAC( LDAFAC, * ), C( LDC, * ),
$ RWORK( * )
* ..
*
* Purpose
* =======
*
* DSYT01 reconstructs a symmetric indefinite matrix A from its
* block L*D*L' or U*D*U' factorization and computes the residual
* norm( C - A ) / ( N * norm(A) * EPS ),
* where C is the reconstructed matrix and EPS is the machine epsilon.
*
* Arguments
* ==========
*
* UPLO (input) CHARACTER*1
* Specifies whether the upper or lower triangular part of the
* symmetric matrix A is stored:
* = 'U': Upper triangular
* = 'L': Lower triangular
*
* N (input) INTEGER
* The number of rows and columns of the matrix A. N >= 0.
*
* A (input) DOUBLE PRECISION array, dimension (LDA,N)
* The original symmetric matrix A.
*
* LDA (input) INTEGER
* The leading dimension of the array A. LDA >= max(1,N)
*
* AFAC (input) DOUBLE PRECISION array, dimension (LDAFAC,N)
* The factored form of the matrix A. AFAC contains the block
* diagonal matrix D and the multipliers used to obtain the
* factor L or U from the block L*D*L' or U*D*U' factorization
* as computed by DSYTRF.
*
* LDAFAC (input) INTEGER
* The leading dimension of the array AFAC. LDAFAC >= max(1,N).
*
* IPIV (input) INTEGER array, dimension (N)
* The pivot indices from DSYTRF.
*
* C (workspace) DOUBLE PRECISION array, dimension (LDC,N)
*
* LDC (integer) INTEGER
* The leading dimension of the array C. LDC >= max(1,N).
*
* RWORK (workspace) DOUBLE PRECISION array, dimension (N)
*
* RESID (output) 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 )
*
* =====================================================================
*
* .. Parameters ..
DOUBLE PRECISION ZERO, ONE
PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0 )
* ..
* .. Local Scalars ..
INTEGER I, INFO, J
DOUBLE PRECISION ANORM, EPS
* ..
* .. External Functions ..
LOGICAL LSAME
DOUBLE PRECISION DLAMCH, DLANSY
EXTERNAL LSAME, DLAMCH, DLANSY
* ..
* .. External Subroutines ..
EXTERNAL DLASET, DLAVSY
* ..
* .. Intrinsic Functions ..
INTRINSIC DBLE
* ..
* .. Executable Statements ..
*
* Quick exit if N = 0.
*
IF( N.LE.0 ) THEN
RESID = ZERO
RETURN
END IF
*
* Determine EPS and the norm of A.
*
EPS = DLAMCH( 'Epsilon' )
ANORM = DLANSY( '1', UPLO, N, A, LDA, RWORK )
*
* Initialize C to the identity matrix.
*
CALL DLASET( 'Full', N, N, ZERO, ONE, C, LDC )
*
* Call DLAVSY to form the product D * U' (or D * L' ).
*
CALL DLAVSY( UPLO, 'Transpose', 'Non-unit', N, N, AFAC, LDAFAC,
$ IPIV, C, LDC, INFO )
*
* Call DLAVSY again to multiply by U (or L ).
*
CALL DLAVSY( UPLO, 'No transpose', 'Unit', N, N, AFAC, LDAFAC,
$ IPIV, C, LDC, INFO )
*
* Compute the difference C - A .
*
IF( LSAME( UPLO, 'U' ) ) THEN
DO 20 J = 1, N
DO 10 I = 1, J
C( I, J ) = C( I, J ) - A( I, J )
10 CONTINUE
20 CONTINUE
ELSE
DO 40 J = 1, N
DO 30 I = J, N
C( I, J ) = C( I, J ) - A( I, J )
30 CONTINUE
40 CONTINUE
END IF
*
* Compute norm( C - A ) / ( N * norm(A) * EPS )
*
RESID = DLANSY( '1', UPLO, N, C, LDC, RWORK )
*
IF( ANORM.LE.ZERO ) THEN
IF( RESID.NE.ZERO )
$ RESID = ONE / EPS
ELSE
RESID = ( ( RESID / DBLE( N ) ) / ANORM ) / EPS
END IF
*
RETURN
*
* End of DSYT01
*
END
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