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Diffstat (limited to '2.3-1/src/fortran/lapack/dlarzt.f')
| -rw-r--r-- | 2.3-1/src/fortran/lapack/dlarzt.f | 184 |
1 files changed, 184 insertions, 0 deletions
diff --git a/2.3-1/src/fortran/lapack/dlarzt.f b/2.3-1/src/fortran/lapack/dlarzt.f new file mode 100644 index 00000000..d79636e0 --- /dev/null +++ b/2.3-1/src/fortran/lapack/dlarzt.f @@ -0,0 +1,184 @@ + SUBROUTINE DLARZT( DIRECT, STOREV, N, K, V, LDV, TAU, T, LDT ) +* +* -- LAPACK routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + CHARACTER DIRECT, STOREV + INTEGER K, LDT, LDV, N +* .. +* .. Array Arguments .. + DOUBLE PRECISION T( LDT, * ), TAU( * ), V( LDV, * ) +* .. +* +* Purpose +* ======= +* +* DLARZT forms the triangular factor T of a real block reflector +* H of order > n, which is defined as a product of k elementary +* reflectors. +* +* If DIRECT = 'F', H = H(1) H(2) . . . H(k) and T is upper triangular; +* +* If DIRECT = 'B', H = H(k) . . . H(2) H(1) and T is lower triangular. +* +* If STOREV = 'C', the vector which defines the elementary reflector +* H(i) is stored in the i-th column of the array V, and +* +* H = I - V * T * V' +* +* If STOREV = 'R', the vector which defines the elementary reflector +* H(i) is stored in the i-th row of the array V, and +* +* H = I - V' * T * V +* +* Currently, only STOREV = 'R' and DIRECT = 'B' are supported. +* +* Arguments +* ========= +* +* DIRECT (input) CHARACTER*1 +* Specifies the order in which the elementary reflectors are +* multiplied to form the block reflector: +* = 'F': H = H(1) H(2) . . . H(k) (Forward, not supported yet) +* = 'B': H = H(k) . . . H(2) H(1) (Backward) +* +* STOREV (input) CHARACTER*1 +* Specifies how the vectors which define the elementary +* reflectors are stored (see also Further Details): +* = 'C': columnwise (not supported yet) +* = 'R': rowwise +* +* N (input) INTEGER +* The order of the block reflector H. N >= 0. +* +* K (input) INTEGER +* The order of the triangular factor T (= the number of +* elementary reflectors). K >= 1. +* +* V (input/output) DOUBLE PRECISION array, dimension +* (LDV,K) if STOREV = 'C' +* (LDV,N) if STOREV = 'R' +* The matrix V. See further details. +* +* LDV (input) INTEGER +* The leading dimension of the array V. +* If STOREV = 'C', LDV >= max(1,N); if STOREV = 'R', LDV >= K. +* +* TAU (input) DOUBLE PRECISION array, dimension (K) +* TAU(i) must contain the scalar factor of the elementary +* reflector H(i). +* +* T (output) DOUBLE PRECISION array, dimension (LDT,K) +* The k by k triangular factor T of the block reflector. +* If DIRECT = 'F', T is upper triangular; if DIRECT = 'B', T is +* lower triangular. The rest of the array is not used. +* +* LDT (input) INTEGER +* The leading dimension of the array T. LDT >= K. +* +* Further Details +* =============== +* +* Based on contributions by +* A. Petitet, Computer Science Dept., Univ. of Tenn., Knoxville, USA +* +* 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_____ +* ( v1 v2 v3 ) / \ +* ( v1 v2 v3 ) ( v1 v1 v1 v1 v1 . . . . 1 ) +* V = ( v1 v2 v3 ) ( v2 v2 v2 v2 v2 . . . 1 ) +* ( v1 v2 v3 ) ( v3 v3 v3 v3 v3 . . 1 ) +* ( v1 v2 v3 ) +* . . . +* . . . +* 1 . . +* 1 . +* 1 +* +* DIRECT = 'B' and STOREV = 'C': DIRECT = 'B' and STOREV = 'R': +* +* ______V_____ +* 1 / \ +* . 1 ( 1 . . . . v1 v1 v1 v1 v1 ) +* . . 1 ( . 1 . . . v2 v2 v2 v2 v2 ) +* . . . ( . . 1 . . v3 v3 v3 v3 v3 ) +* . . . +* ( v1 v2 v3 ) +* ( v1 v2 v3 ) +* V = ( v1 v2 v3 ) +* ( v1 v2 v3 ) +* ( v1 v2 v3 ) +* +* ===================================================================== +* +* .. Parameters .. + DOUBLE PRECISION ZERO + PARAMETER ( ZERO = 0.0D+0 ) +* .. +* .. Local Scalars .. + INTEGER I, INFO, J +* .. +* .. External Subroutines .. + EXTERNAL DGEMV, DTRMV, XERBLA +* .. +* .. External Functions .. + LOGICAL LSAME + EXTERNAL LSAME +* .. +* .. Executable Statements .. +* +* Check for currently supported options +* + INFO = 0 + IF( .NOT.LSAME( DIRECT, 'B' ) ) THEN + INFO = -1 + ELSE IF( .NOT.LSAME( STOREV, 'R' ) ) THEN + INFO = -2 + END IF + IF( INFO.NE.0 ) THEN + CALL XERBLA( 'DLARZT', -INFO ) + RETURN + END IF +* + DO 20 I = K, 1, -1 + IF( TAU( I ).EQ.ZERO ) THEN +* +* H(i) = I +* + DO 10 J = I, K + T( J, I ) = ZERO + 10 CONTINUE + ELSE +* +* general case +* + IF( I.LT.K ) THEN +* +* T(i+1:k,i) = - tau(i) * V(i+1:k,1:n) * V(i,1:n)' +* + CALL DGEMV( 'No transpose', K-I, N, -TAU( I ), + $ V( I+1, 1 ), LDV, V( I, 1 ), LDV, ZERO, + $ T( I+1, I ), 1 ) +* +* T(i+1:k,i) = T(i+1:k,i+1:k) * T(i+1:k,i) +* + CALL DTRMV( 'Lower', 'No transpose', 'Non-unit', K-I, + $ T( I+1, I+1 ), LDT, T( I+1, I ), 1 ) + END IF + T( I, I ) = TAU( I ) + END IF + 20 CONTINUE + RETURN +* +* End of DLARZT +* + END |