From 9cf77ce1d80cf17aa79c5da95b578ee2a4490152 Mon Sep 17 00:00:00 2001 From: Desire NUENTSA Date: Mon, 12 Nov 2012 15:20:37 +0100 Subject: Add support for Sparse QR factorization --- lapack/clarfg.f | 203 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 203 insertions(+) create mode 100644 lapack/clarfg.f (limited to 'lapack/clarfg.f') diff --git a/lapack/clarfg.f b/lapack/clarfg.f new file mode 100644 index 000000000..d64f396c3 --- /dev/null +++ b/lapack/clarfg.f @@ -0,0 +1,203 @@ +*> \brief \b CLARFG +* +* =========== DOCUMENTATION =========== +* +* Online html documentation available at +* http://www.netlib.org/lapack/explore-html/ +* +*> \htmlonly +*> Download CLARFG + dependencies +*> +*> [TGZ] +*> +*> [ZIP] +*> +*> [TXT] +*> \endhtmlonly +* +* Definition: +* =========== +* +* SUBROUTINE CLARFG( N, ALPHA, X, INCX, TAU ) +* +* .. Scalar Arguments .. +* INTEGER INCX, N +* COMPLEX ALPHA, TAU +* .. +* .. Array Arguments .. +* COMPLEX X( * ) +* .. +* +* +*> \par Purpose: +* ============= +*> +*> \verbatim +*> +*> CLARFG generates a complex elementary reflector H of order n, such +*> that +*> +*> H**H * ( alpha ) = ( beta ), H**H * H = I. +*> ( x ) ( 0 ) +*> +*> where alpha and beta are scalars, with beta real, and x is an +*> (n-1)-element complex vector. H is represented in the form +*> +*> H = I - tau * ( 1 ) * ( 1 v**H ) , +*> ( v ) +*> +*> where tau is a complex scalar and v is a complex (n-1)-element +*> vector. Note that H is not hermitian. +*> +*> If the elements of x are all zero and alpha is real, then tau = 0 +*> and H is taken to be the unit matrix. +*> +*> Otherwise 1 <= real(tau) <= 2 and abs(tau-1) <= 1 . +*> \endverbatim +* +* Arguments: +* ========== +* +*> \param[in] N +*> \verbatim +*> N is INTEGER +*> The order of the elementary reflector. +*> \endverbatim +*> +*> \param[in,out] ALPHA +*> \verbatim +*> ALPHA is COMPLEX +*> On entry, the value alpha. +*> On exit, it is overwritten with the value beta. +*> \endverbatim +*> +*> \param[in,out] X +*> \verbatim +*> X is COMPLEX array, dimension +*> (1+(N-2)*abs(INCX)) +*> On entry, the vector x. +*> On exit, it is overwritten with the vector v. +*> \endverbatim +*> +*> \param[in] INCX +*> \verbatim +*> INCX is INTEGER +*> The increment between elements of X. INCX > 0. +*> \endverbatim +*> +*> \param[out] TAU +*> \verbatim +*> TAU is COMPLEX +*> The value tau. +*> \endverbatim +* +* Authors: +* ======== +* +*> \author Univ. of Tennessee +*> \author Univ. of California Berkeley +*> \author Univ. of Colorado Denver +*> \author NAG Ltd. +* +*> \date November 2011 +* +*> \ingroup complexOTHERauxiliary +* +* ===================================================================== + SUBROUTINE CLARFG( N, ALPHA, X, INCX, TAU ) +* +* -- LAPACK auxiliary routine (version 3.4.0) -- +* -- LAPACK is a software package provided by Univ. of Tennessee, -- +* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- +* November 2011 +* +* .. Scalar Arguments .. + INTEGER INCX, N + COMPLEX ALPHA, TAU +* .. +* .. Array Arguments .. + COMPLEX X( * ) +* .. +* +* ===================================================================== +* +* .. Parameters .. + REAL ONE, ZERO + PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 ) +* .. +* .. Local Scalars .. + INTEGER J, KNT + REAL ALPHI, ALPHR, BETA, RSAFMN, SAFMIN, XNORM +* .. +* .. External Functions .. + REAL SCNRM2, SLAMCH, SLAPY3 + COMPLEX CLADIV + EXTERNAL SCNRM2, SLAMCH, SLAPY3, CLADIV +* .. +* .. Intrinsic Functions .. + INTRINSIC ABS, AIMAG, CMPLX, REAL, SIGN +* .. +* .. External Subroutines .. + EXTERNAL CSCAL, CSSCAL +* .. +* .. Executable Statements .. +* + IF( N.LE.0 ) THEN + TAU = ZERO + RETURN + END IF +* + XNORM = SCNRM2( N-1, X, INCX ) + ALPHR = REAL( ALPHA ) + ALPHI = AIMAG( ALPHA ) +* + IF( XNORM.EQ.ZERO .AND. ALPHI.EQ.ZERO ) THEN +* +* H = I +* + TAU = ZERO + ELSE +* +* general case +* + BETA = -SIGN( SLAPY3( ALPHR, ALPHI, XNORM ), ALPHR ) + SAFMIN = SLAMCH( 'S' ) / SLAMCH( 'E' ) + RSAFMN = ONE / SAFMIN +* + KNT = 0 + IF( ABS( BETA ).LT.SAFMIN ) THEN +* +* XNORM, BETA may be inaccurate; scale X and recompute them +* + 10 CONTINUE + KNT = KNT + 1 + CALL CSSCAL( N-1, RSAFMN, X, INCX ) + BETA = BETA*RSAFMN + ALPHI = ALPHI*RSAFMN + ALPHR = ALPHR*RSAFMN + IF( ABS( BETA ).LT.SAFMIN ) + $ GO TO 10 +* +* New BETA is at most 1, at least SAFMIN +* + XNORM = SCNRM2( N-1, X, INCX ) + ALPHA = CMPLX( ALPHR, ALPHI ) + BETA = -SIGN( SLAPY3( ALPHR, ALPHI, XNORM ), ALPHR ) + END IF + TAU = CMPLX( ( BETA-ALPHR ) / BETA, -ALPHI / BETA ) + ALPHA = CLADIV( CMPLX( ONE ), ALPHA-BETA ) + CALL CSCAL( N-1, ALPHA, X, INCX ) +* +* If ALPHA is subnormal, it may lose relative accuracy +* + DO 20 J = 1, KNT + BETA = BETA*SAFMIN + 20 CONTINUE + ALPHA = BETA + END IF +* + RETURN +* +* End of CLARFG +* + END -- cgit v1.2.3