dlarfb
C DLARFB SOURCE BP208322 20/09/18 21:16:04 10718 *> \brief \b DLARFB applies a block reflector or its transpose to a general rectangular matrix. * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * *> \htmlonly *> Download DLARFB + dependencies *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlarfb.f"> *> [TGZ]</a> *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlarfb.f"> *> [ZIP]</a> *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlarfb.f"> *> [TXT]</a> *> \endhtmlonly * * Definition: * =========== * * SUBROUTINE DLARFB( SIDE, TRANS, DIRECT, STOREV, M, N, K, V, LDV, * T, LDT, C, LDC, WORK, LDWORK ) * * .. Scalar Arguments .. * CHARACTER DIRECT, SIDE, STOREV, TRANS * INTEGER K, LDC, LDT, LDV, LDWORK, M, N * .. * .. Array Arguments .. * REAL*8 C( LDC, * ), T( LDT, * ), V( LDV, * ), * $ WORK( LDWORK, * ) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> DLARFB applies a real block reflector H or its transpose H**T to a *> real m by n matrix C, from either the left or the right. *> \endverbatim * * Arguments: * ========== * *> \param[in] SIDE *> \verbatim *> SIDE is CHARACTER*1 *> = 'L': apply H or H**T from the Left *> = 'R': apply H or H**T from the Right *> \endverbatim *> *> \param[in] TRANS *> \verbatim *> TRANS is CHARACTER*1 *> = 'N': apply H (No transpose) *> = 'T': apply H**T (Transpose) *> \endverbatim *> *> \param[in] DIRECT *> \verbatim *> DIRECT is CHARACTER*1 *> Indicates how H is formed from a product of elementary *> reflectors *> = 'F': H = H(1) H(2) . . . H(k) (Forward) *> = 'B': H = H(k) . . . H(2) H(1) (Backward) *> \endverbatim *> *> \param[in] STOREV *> \verbatim *> STOREV is CHARACTER*1 *> Indicates how the vectors which define the elementary *> reflectors are stored: *> = 'C': Columnwise *> = 'R': Rowwise *> \endverbatim *> *> \param[in] M *> \verbatim *> M is INTEGER *> The number of rows of the matrix C. *> \endverbatim *> *> \param[in] N *> \verbatim *> N is INTEGER *> The number of columns of the matrix C. *> \endverbatim *> *> \param[in] K *> \verbatim *> K is INTEGER *> The order of the matrix T (= the number of elementary *> reflectors whose product defines the block reflector). *> \endverbatim *> *> \param[in] V *> \verbatim *> V is REAL*8 array, dimension *> (LDV,K) if STOREV = 'C' *> (LDV,M) if STOREV = 'R' and SIDE = 'L' *> (LDV,N) if STOREV = 'R' and SIDE = 'R' *> The matrix V. See Further Details. *> \endverbatim *> *> \param[in] LDV *> \verbatim *> LDV is INTEGER *> The leading dimension of the array V. *> If STOREV = 'C' and SIDE = 'L', LDV >= max(1,M); *> if STOREV = 'C' and SIDE = 'R', LDV >= max(1,N); *> if STOREV = 'R', LDV >= K. *> \endverbatim *> *> \param[in] T *> \verbatim *> T is REAL*8 array, dimension (LDT,K) *> The triangular k by k matrix T in the representation of the *> block reflector. *> \endverbatim *> *> \param[in] LDT *> \verbatim *> LDT is INTEGER *> The leading dimension of the array T. LDT >= K. *> \endverbatim *> *> \param[in,out] C *> \verbatim *> C is REAL*8 array, dimension (LDC,N) *> On entry, the m by n matrix C. *> On exit, C is overwritten by H*C or H**T*C or C*H or C*H**T. *> \endverbatim *> *> \param[in] LDC *> \verbatim *> LDC is INTEGER *> The leading dimension of the array C. LDC >= max(1,M). *> \endverbatim *> *> \param[out] WORK *> \verbatim *> WORK is REAL*8 array, dimension (LDWORK,K) *> \endverbatim *> *> \param[in] LDWORK *> \verbatim *> LDWORK is INTEGER *> The leading dimension of the array WORK. *> If SIDE = 'L', LDWORK >= max(1,N); *> if SIDE = 'R', LDWORK >= max(1,M). *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \date June 2013 * *> \ingroup doubleOTHERauxiliary * *> \par Further Details: * ===================== *> *> \verbatim *> *> The shape of the matrix V and the storage of the vectors which define *> the H(i) is best illustrated by the following example with n = 5 and *> k = 3. The elements equal to 1 are not stored; the corresponding *> array elements are modified but restored on exit. The rest of the *> array is not used. *> *> DIRECT = 'F' and STOREV = 'C': DIRECT = 'F' and STOREV = 'R': *> *> V = ( 1 ) V = ( 1 v1 v1 v1 v1 ) *> ( v1 1 ) ( 1 v2 v2 v2 ) *> ( v1 v2 1 ) ( 1 v3 v3 ) *> ( v1 v2 v3 ) *> ( v1 v2 v3 ) *> *> DIRECT = 'B' and STOREV = 'C': DIRECT = 'B' and STOREV = 'R': *> *> V = ( v1 v2 v3 ) V = ( v1 v1 1 ) *> ( v1 v2 v3 ) ( v2 v2 v2 1 ) *> ( 1 v2 v3 ) ( v3 v3 v3 v3 1 ) *> ( 1 v3 ) *> ( 1 ) *> \endverbatim *> * ===================================================================== $ T, LDT, C, LDC, WORK, LDWORK ) * * -- LAPACK auxdtiliary routine (version 3.7.0) -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * June 2013 IMPLICIT INTEGER(I-N) IMPLICIT REAL*8(A-H,O-Z) * * .. Scalar Arguments .. CHARACTER DIRECT, SIDE, STOREV, TRANS INTEGER K, LDC, LDT, LDV, LDWORK, M, N * .. * .. Array Arguments .. REAL*8 C( LDC, * ), T( LDT, * ), V( LDV, * ), * .. * * ===================================================================== * * .. Parameters .. REAL*8 ONE PARAMETER ( ONE = 1.0D+0 ) * .. * .. Local Scalars .. CHARACTER TRANST INTEGER I, J * .. * .. External Functions .. LOGICAL LSAME * EXTERNAL LSAME * .. * .. External Subroutines .. * EXTERNAL DCOPY, DGEMM, DTRMM * .. * .. Executable Statements .. * * Quick return if possible * IF( M.LE.0 .OR. N.LE.0 ) $ RETURN * TRANST = 'T' ELSE TRANST = 'N' END IF * * * * Let V = ( V1 ) (first K rows) * ( V2 ) * where V1 is unit lower triangular. * * * Form H * C or H**T * C where C = ( C1 ) * ( C2 ) * * W := C**T * V = (C1**T * V1 + C2**T * V2) (stored in WORK) * * W := C1**T * DO 10 J = 1, K 10 CONTINUE * * W := W * V1 * $ K, ONE, V, LDV, WORK, LDWORK ) IF( M.GT.K ) THEN * * W := W + C2**T * V2 * $ ONE, C( K+1, 1 ), LDC, V( K+1, 1 ), LDV, $ ONE, WORK, LDWORK ) END IF * * W := W * T**T or W * T * $ ONE, T, LDT, WORK, LDWORK ) * * C := C - V * W**T * IF( M.GT.K ) THEN * * C2 := C2 - V2 * W**T * $ C( K+1, 1 ), LDC ) END IF * * W := W * V1**T * $ ONE, V, LDV, WORK, LDWORK ) * * C1 := C1 - W**T * DO 30 J = 1, K DO 20 I = 1, N 20 CONTINUE 30 CONTINUE * * * Form C * H or C * H**T where C = ( C1 C2 ) * * W := C * V = (C1*V1 + C2*V2) (stored in WORK) * * W := C1 * DO 40 J = 1, K 40 CONTINUE * * W := W * V1 * $ K, ONE, V, LDV, WORK, LDWORK ) IF( N.GT.K ) THEN * * W := W + C2 * V2 * $ ONE, C( 1, K+1 ), LDC, V( K+1, 1 ), LDV, $ ONE, WORK, LDWORK ) END IF * * W := W * T or W * T**T * $ ONE, T, LDT, WORK, LDWORK ) * * C := C - W * V**T * IF( N.GT.K ) THEN * * C2 := C2 - W * V2**T * $ C( 1, K+1 ), LDC ) END IF * * W := W * V1**T * $ ONE, V, LDV, WORK, LDWORK ) * * C1 := C1 - W * DO 60 J = 1, K DO 50 I = 1, M 50 CONTINUE 60 CONTINUE END IF * ELSE * * Let V = ( V1 ) * ( V2 ) (last K rows) * where V2 is unit upper triangular. * * * Form H * C or H**T * C where C = ( C1 ) * ( C2 ) * * W := C**T * V = (C1**T * V1 + C2**T * V2) (stored in WORK) * * W := C2**T * DO 70 J = 1, K 70 CONTINUE * * W := W * V2 * IF( M.GT.K ) THEN * * W := W + C1**T * V1 * $ ONE, C, LDC, V, LDV, ONE, WORK, LDWORK ) END IF * * W := W * T**T or W * T * $ ONE, T, LDT, WORK, LDWORK ) * * C := C - V * W**T * IF( M.GT.K ) THEN * * C1 := C1 - V1 * W**T * END IF * * W := W * V2**T * * * C2 := C2 - W**T * DO 90 J = 1, K DO 80 I = 1, N 80 CONTINUE 90 CONTINUE * * * Form C * H or C * H**T where C = ( C1 C2 ) * * W := C * V = (C1*V1 + C2*V2) (stored in WORK) * * W := C2 * DO 100 J = 1, K 100 CONTINUE * * W := W * V2 * IF( N.GT.K ) THEN * * W := W + C1 * V1 * $ ONE, C, LDC, V, LDV, ONE, WORK, LDWORK ) END IF * * W := W * T or W * T**T * $ ONE, T, LDT, WORK, LDWORK ) * * C := C - W * V**T * IF( N.GT.K ) THEN * * C1 := C1 - W * V1**T * END IF * * W := W * V2**T * * * C2 := C2 - W * DO 120 J = 1, K DO 110 I = 1, M 110 CONTINUE 120 CONTINUE END IF END IF * * * * Let V = ( V1 V2 ) (V1: first K columns) * where V1 is unit upper triangular. * * * Form H * C or H**T * C where C = ( C1 ) * ( C2 ) * * W := C**T * V**T = (C1**T * V1**T + C2**T * V2**T) (stored in WORK) * * W := C1**T * DO 130 J = 1, K 130 CONTINUE * * W := W * V1**T * $ ONE, V, LDV, WORK, LDWORK ) IF( M.GT.K ) THEN * * W := W + C2**T * V2**T * $ C( K+1, 1 ), LDC, V( 1, K+1 ), LDV, ONE, $ WORK, LDWORK ) END IF * * W := W * T**T or W * T * $ ONE, T, LDT, WORK, LDWORK ) * * C := C - V**T * W**T * IF( M.GT.K ) THEN * * C2 := C2 - V2**T * W**T * $ C( K+1, 1 ), LDC ) END IF * * W := W * V1 * $ K, ONE, V, LDV, WORK, LDWORK ) * * C1 := C1 - W**T * DO 150 J = 1, K DO 140 I = 1, N 140 CONTINUE 150 CONTINUE * * * Form C * H or C * H**T where C = ( C1 C2 ) * * W := C * V**T = (C1*V1**T + C2*V2**T) (stored in WORK) * * W := C1 * DO 160 J = 1, K 160 CONTINUE * * W := W * V1**T * $ ONE, V, LDV, WORK, LDWORK ) IF( N.GT.K ) THEN * * W := W + C2 * V2**T * $ ONE, C( 1, K+1 ), LDC, V( 1, K+1 ), LDV, $ ONE, WORK, LDWORK ) END IF * * W := W * T or W * T**T * $ ONE, T, LDT, WORK, LDWORK ) * * C := C - W * V * IF( N.GT.K ) THEN * * C2 := C2 - W * V2 * $ C( 1, K+1 ), LDC ) END IF * * W := W * V1 * $ K, ONE, V, LDV, WORK, LDWORK ) * * C1 := C1 - W * DO 180 J = 1, K DO 170 I = 1, M 170 CONTINUE 180 CONTINUE * END IF * ELSE * * Let V = ( V1 V2 ) (V2: last K columns) * where V2 is unit lower triangular. * * * Form H * C or H**T * C where C = ( C1 ) * ( C2 ) * * W := C**T * V**T = (C1**T * V1**T + C2**T * V2**T) (stored in WORK) * * W := C2**T * DO 190 J = 1, K 190 CONTINUE * * W := W * V2**T * IF( M.GT.K ) THEN * * W := W + C1**T * V1**T * $ C, LDC, V, LDV, ONE, WORK, LDWORK ) END IF * * W := W * T**T or W * T * $ ONE, T, LDT, WORK, LDWORK ) * * C := C - V**T * W**T * IF( M.GT.K ) THEN * * C1 := C1 - V1**T * W**T * $ V, LDV, WORK, LDWORK, ONE, C, LDC ) END IF * * W := W * V2 * * * C2 := C2 - W**T * DO 210 J = 1, K DO 200 I = 1, N 200 CONTINUE 210 CONTINUE * * * Form C * H or C * H' where C = ( C1 C2 ) * * W := C * V**T = (C1*V1**T + C2*V2**T) (stored in WORK) * * W := C2 * DO 220 J = 1, K 220 CONTINUE * * W := W * V2**T * IF( N.GT.K ) THEN * * W := W + C1 * V1**T * $ ONE, C, LDC, V, LDV, ONE, WORK, LDWORK ) END IF * * W := W * T or W * T**T * $ ONE, T, LDT, WORK, LDWORK ) * * C := C - W * V * IF( N.GT.K ) THEN * * C1 := C1 - W * V1 * END IF * * W := W * V2 * * * C1 := C1 - W * DO 240 J = 1, K DO 230 I = 1, M 230 CONTINUE 240 CONTINUE * END IF * END IF END IF * RETURN * * End of DLARFB * END
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