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LAPACK
3.7.0
LAPACK: Linear Algebra PACKage
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subroutine dlarfb | ( | character | SIDE, |
character | TRANS, | ||
character | DIRECT, | ||
character | STOREV, | ||
integer | M, | ||
integer | N, | ||
integer | K, | ||
double precision, dimension( ldv, * ) | V, | ||
integer | LDV, | ||
double precision, dimension( ldt, * ) | T, | ||
integer | LDT, | ||
double precision, dimension( ldc, * ) | C, | ||
integer | LDC, | ||
double precision, dimension( ldwork, * ) | WORK, | ||
integer | LDWORK | ||
) |
DLARFB applies a block reflector or its transpose to a general rectangular matrix.
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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.
[in] | SIDE | SIDE is CHARACTER*1 = 'L': apply H or H**T from the Left = 'R': apply H or H**T from the Right |
[in] | TRANS | TRANS is CHARACTER*1 = 'N': apply H (No transpose) = 'T': apply H**T (Transpose) |
[in] | DIRECT | 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) |
[in] | STOREV | STOREV is CHARACTER*1 Indicates how the vectors which define the elementary reflectors are stored: = 'C': Columnwise = 'R': Rowwise |
[in] | M | M is INTEGER The number of rows of the matrix C. |
[in] | N | N is INTEGER The number of columns of the matrix C. |
[in] | K | K is INTEGER The order of the matrix T (= the number of elementary reflectors whose product defines the block reflector). |
[in] | V | V is DOUBLE PRECISION 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. |
[in] | LDV | 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. |
[in] | T | T is DOUBLE PRECISION array, dimension (LDT,K) The triangular k by k matrix T in the representation of the block reflector. |
[in] | LDT | LDT is INTEGER The leading dimension of the array T. LDT >= K. |
[in,out] | C | C is DOUBLE PRECISION 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. |
[in] | LDC | LDC is INTEGER The leading dimension of the array C. LDC >= max(1,M). |
[out] | WORK | WORK is DOUBLE PRECISION array, dimension (LDWORK,K) |
[in] | LDWORK | LDWORK is INTEGER The leading dimension of the array WORK. If SIDE = 'L', LDWORK >= max(1,N); if SIDE = 'R', LDWORK >= max(1,M). |
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 )
Definition at line 197 of file dlarfb.f.