diff options
Diffstat (limited to '2.3-1/src/fortran/lapack/dlarz.f')
| -rw-r--r-- | 2.3-1/src/fortran/lapack/dlarz.f | 152 |
1 files changed, 152 insertions, 0 deletions
diff --git a/2.3-1/src/fortran/lapack/dlarz.f b/2.3-1/src/fortran/lapack/dlarz.f new file mode 100644 index 00000000..b302fdc2 --- /dev/null +++ b/2.3-1/src/fortran/lapack/dlarz.f @@ -0,0 +1,152 @@ + SUBROUTINE DLARZ( SIDE, M, N, L, V, INCV, TAU, C, LDC, WORK ) +* +* -- LAPACK routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + CHARACTER SIDE + INTEGER INCV, L, LDC, M, N + DOUBLE PRECISION TAU +* .. +* .. Array Arguments .. + DOUBLE PRECISION C( LDC, * ), V( * ), WORK( * ) +* .. +* +* Purpose +* ======= +* +* DLARZ applies a real elementary reflector H to a real M-by-N +* matrix C, from either the left or the right. H is represented in the +* form +* +* H = I - tau * v * v' +* +* where tau is a real scalar and v is a real vector. +* +* If tau = 0, then H is taken to be the unit matrix. +* +* +* H is a product of k elementary reflectors as returned by DTZRZF. +* +* Arguments +* ========= +* +* SIDE (input) CHARACTER*1 +* = 'L': form H * C +* = 'R': form C * H +* +* M (input) INTEGER +* The number of rows of the matrix C. +* +* N (input) INTEGER +* The number of columns of the matrix C. +* +* L (input) INTEGER +* The number of entries of the vector V containing +* the meaningful part of the Householder vectors. +* If SIDE = 'L', M >= L >= 0, if SIDE = 'R', N >= L >= 0. +* +* V (input) DOUBLE PRECISION array, dimension (1+(L-1)*abs(INCV)) +* The vector v in the representation of H as returned by +* DTZRZF. V is not used if TAU = 0. +* +* INCV (input) INTEGER +* The increment between elements of v. INCV <> 0. +* +* TAU (input) DOUBLE PRECISION +* The value tau in the representation of H. +* +* C (input/output) DOUBLE PRECISION array, dimension (LDC,N) +* On entry, the M-by-N matrix C. +* On exit, C is overwritten by the matrix H * C if SIDE = 'L', +* or C * H if SIDE = 'R'. +* +* LDC (input) INTEGER +* The leading dimension of the array C. LDC >= max(1,M). +* +* WORK (workspace) DOUBLE PRECISION array, dimension +* (N) if SIDE = 'L' +* or (M) if SIDE = 'R' +* +* Further Details +* =============== +* +* Based on contributions by +* A. Petitet, Computer Science Dept., Univ. of Tenn., Knoxville, USA +* +* ===================================================================== +* +* .. Parameters .. + DOUBLE PRECISION ONE, ZERO + PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 ) +* .. +* .. External Subroutines .. + EXTERNAL DAXPY, DCOPY, DGEMV, DGER +* .. +* .. External Functions .. + LOGICAL LSAME + EXTERNAL LSAME +* .. +* .. Executable Statements .. +* + IF( LSAME( SIDE, 'L' ) ) THEN +* +* Form H * C +* + IF( TAU.NE.ZERO ) THEN +* +* w( 1:n ) = C( 1, 1:n ) +* + CALL DCOPY( N, C, LDC, WORK, 1 ) +* +* w( 1:n ) = w( 1:n ) + C( m-l+1:m, 1:n )' * v( 1:l ) +* + CALL DGEMV( 'Transpose', L, N, ONE, C( M-L+1, 1 ), LDC, V, + $ INCV, ONE, WORK, 1 ) +* +* C( 1, 1:n ) = C( 1, 1:n ) - tau * w( 1:n ) +* + CALL DAXPY( N, -TAU, WORK, 1, C, LDC ) +* +* C( m-l+1:m, 1:n ) = C( m-l+1:m, 1:n ) - ... +* tau * v( 1:l ) * w( 1:n )' +* + CALL DGER( L, N, -TAU, V, INCV, WORK, 1, C( M-L+1, 1 ), + $ LDC ) + END IF +* + ELSE +* +* Form C * H +* + IF( TAU.NE.ZERO ) THEN +* +* w( 1:m ) = C( 1:m, 1 ) +* + CALL DCOPY( M, C, 1, WORK, 1 ) +* +* w( 1:m ) = w( 1:m ) + C( 1:m, n-l+1:n, 1:n ) * v( 1:l ) +* + CALL DGEMV( 'No transpose', M, L, ONE, C( 1, N-L+1 ), LDC, + $ V, INCV, ONE, WORK, 1 ) +* +* C( 1:m, 1 ) = C( 1:m, 1 ) - tau * w( 1:m ) +* + CALL DAXPY( M, -TAU, WORK, 1, C, 1 ) +* +* C( 1:m, n-l+1:n ) = C( 1:m, n-l+1:n ) - ... +* tau * w( 1:m ) * v( 1:l )' +* + CALL DGER( M, L, -TAU, WORK, 1, V, INCV, C( 1, N-L+1 ), + $ LDC ) +* + END IF +* + END IF +* + RETURN +* +* End of DLARZ +* + END |