cla_syrcond_x()

real function cla_syrcond_x	(	character	uplo,
		integer	n,
		complex, dimension( lda, * )	a,
		integer	lda,
		complex, dimension( ldaf, * )	af,
		integer	ldaf,
		integer, dimension( * )	ipiv,
		complex, dimension( * )	x,
		integer	info,
		complex, dimension( * )	work,
		real, dimension( * )	rwork
	)

CLA_SYRCOND_X computes the infinity norm condition number of op(A)*diag(x) for symmetric indefinite matrices.

Download CLA_SYRCOND_X + dependencies [TGZ] [ZIP] [TXT]

Purpose:

    CLA_SYRCOND_X Computes the infinity norm condition number of
    op(A) * diag(X) where X is a COMPLEX vector.

Parameters

[in]	UPLO	UPLO is CHARACTER*1 = 'U': Upper triangle of A is stored; = 'L': Lower triangle of A is stored.
[in]	N	N is INTEGER The number of linear equations, i.e., the order of the matrix A. N >= 0.
[in]	A	A is COMPLEX array, dimension (LDA,N) On entry, the N-by-N matrix A.
[in]	LDA	LDA is INTEGER The leading dimension of the array A. LDA >= max(1,N).
[in]	AF	AF is COMPLEX array, dimension (LDAF,N) The block diagonal matrix D and the multipliers used to obtain the factor U or L as computed by CSYTRF.
[in]	LDAF	LDAF is INTEGER The leading dimension of the array AF. LDAF >= max(1,N).
[in]	IPIV	IPIV is INTEGER array, dimension (N) Details of the interchanges and the block structure of D as determined by CSYTRF.
[in]	X	X is COMPLEX array, dimension (N) The vector X in the formula op(A) * diag(X).
[out]	INFO	INFO is INTEGER = 0: Successful exit. i > 0: The ith argument is invalid.
[out]	WORK	WORK is COMPLEX array, dimension (2*N). Workspace.
[out]	RWORK	RWORK is REAL array, dimension (N). Workspace.

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 129 of file cla_syrcond_x.f.

*
*  -- LAPACK computational 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            N, LDA, LDAF, INFO
*     ..
*     .. Array Arguments ..
      INTEGER            IPIV( * )
      COMPLEX            A( LDA, * ), AF( LDAF, * ), WORK( * ), X( * )
      REAL               RWORK( * )
*     ..
*
*  =====================================================================
*
*     .. Local Scalars ..
      INTEGER            KASE
      REAL               AINVNM, ANORM, TMP
      INTEGER            I, J
      LOGICAL            UP, UPPER
      COMPLEX            ZDUM
*     ..
*     .. Local Arrays ..
      INTEGER            ISAVE( 3 )
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           lsame
*     ..
*     .. External Subroutines ..
      EXTERNAL           clacn2, csytrs, xerbla
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          abs, max
*     ..
*     .. Statement Functions ..
      REAL               CABS1
*     ..
*     .. Statement Function Definitions ..
      cabs1( zdum ) = abs( real( zdum ) ) + abs( aimag( zdum ) )
*     ..
*     .. Executable Statements ..
*
      cla_syrcond_x = 0.0e+0
*
      info = 0
      upper = lsame( uplo, 'U' )
      IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
         info = -1
      ELSE IF ( n.LT.0 ) THEN
         info = -2
      ELSE IF( lda.LT.max( 1, n ) ) THEN
         info = -4
      ELSE IF( ldaf.LT.max( 1, n ) ) THEN
         info = -6
      END IF
      IF( info.NE.0 ) THEN
         CALL xerbla( 'CLA_SYRCOND_X', -info )
         RETURN
      END IF
      up = .false.
      IF ( lsame( uplo, 'U' ) ) up = .true.
*
*     Compute norm of op(A)*op2(C).
*
      anorm = 0.0
      IF ( up ) THEN
         DO i = 1, n
            tmp = 0.0e+0
            DO j = 1, i
               tmp = tmp + cabs1( a( j, i ) * x( j ) )
            END DO
            DO j = i+1, n
               tmp = tmp + cabs1( a( i, j ) * x( j ) )
            END DO
            rwork( i ) = tmp
            anorm = max( anorm, tmp )
         END DO
      ELSE
         DO i = 1, n
            tmp = 0.0e+0
            DO j = 1, i
               tmp = tmp + cabs1( a( i, j ) * x( j ) )
            END DO
            DO j = i+1, n
               tmp = tmp + cabs1( a( j, i ) * x( j ) )
            END DO
            rwork( i ) = tmp
            anorm = max( anorm, tmp )
         END DO
      END IF
*
*     Quick return if possible.
*
      IF( n.EQ.0 ) THEN
         cla_syrcond_x = 1.0e+0
         RETURN
      ELSE IF( anorm .EQ. 0.0e+0 ) THEN
         RETURN
      END IF
*
*     Estimate the norm of inv(op(A)).
*
      ainvnm = 0.0e+0
*
      kase = 0
   10 CONTINUE
      CALL clacn2( n, work( n+1 ), work, ainvnm, kase, isave )
      IF( kase.NE.0 ) THEN
         IF( kase.EQ.2 ) THEN
*
*           Multiply by R.
*
            DO i = 1, n
               work( i ) = work( i ) * rwork( i )
            END DO
*
            IF ( up ) THEN
               CALL csytrs( 'U', n, 1, af, ldaf, ipiv,
     $            work, n, info )
            ELSE
               CALL csytrs( 'L', n, 1, af, ldaf, ipiv,
     $            work, n, info )
            ENDIF
*
*           Multiply by inv(X).
*
            DO i = 1, n
               work( i ) = work( i ) / x( i )
            END DO
         ELSE
*
*           Multiply by inv(X**T).
*
            DO i = 1, n
               work( i ) = work( i ) / x( i )
            END DO
*
            IF ( up ) THEN
               CALL csytrs( 'U', n, 1, af, ldaf, ipiv,
     $            work, n, info )
            ELSE
               CALL csytrs( 'L', n, 1, af, ldaf, ipiv,
     $            work, n, info )
            END IF
*
*           Multiply by R.
*
            DO i = 1, n
               work( i ) = work( i ) * rwork( i )
            END DO
         END IF
         GO TO 10
      END IF
*
*     Compute the estimate of the reciprocal condition number.
*
      IF( ainvnm .NE. 0.0e+0 )
     $   cla_syrcond_x = 1.0e+0 / ainvnm
*
      RETURN
*
*     End of CLA_SYRCOND_X
*

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