LARZB - 5.2 English - 68552

AOCL API Guide (68552)
Document ID
68552
Release Date
2025-12-29
Version
5.2 English
template<typename T>
void larzb(char *side, char *trans, char *direct, char *storev, integer *m, integer *n, integer *k, integer *l, T *v, integer *ldv, T *t, integer *ldt, T *c, integer *ldc, T *work, integer *ldwork)#

LARZB applies a block reflector or its transpose to a general matrix.

Purpose: 

 LARZB applies a real block reflector H or its transpose H**T to
 a real distributed M-by-N  C from the left or the right.

 Currently, only STOREV = 'R' and DIRECT = 'B' are supported.
Parameters:

  • SIDE – [in]

    SIDE is CHARACTER*1

    = ‘L’: apply H or H**T from the Left

    = ‘R’: apply H or H**T from the Right

  • TRANS – [in]

    TRANS is CHARACTER*1

    = ‘N’: apply H (No transpose)

    = ‘C’: apply H**T (Transpose)

  • DIRECT – [in]

    DIRECT is CHARACTER*1

    Indicates how H is formed from a product of elementary reflectors

    = ‘F’: H = H(1) H(2) … H(k) (Forward, not supported yet)

    = ‘B’: H = H(k) … H(2) H(1) (Backward)

  • STOREV – [in]

    STOREV is CHARACTER*1

    Indicates how the vectors which define the elementary reflectors are stored:

    = ‘C’: Columnwise (not supported yet)

    = ‘R’: Rowwise

  • M – [in]

    M is INTEGER

    The number of rows of the matrix C.

  • N – [in]

    N is INTEGER

    The number of columns of the matrix C.

  • K – [in]

    K is INTEGER

    The order of the matrix T (= the number of elementary reflectors whose product defines the block reflector).

  • L – [in]

    L is INTEGER

    The number of columns of the matrix V containing the meaningful part of the Householder reflectors.

    If SIDE = ‘L’, M >= L >= 0, if SIDE = ‘R’, N >= L >= 0.

  • V – [in]

    V is REAL array, dimension (LDV,NV).

    If STOREV = ‘C’, NV = K; if STOREV = ‘R’, NV = L.

  • LDV – [in]

    LDV is INTEGER

    The leading dimension of the array V.

    If STOREV = ‘C’, LDV >= L; if STOREV = ‘R’, LDV >= K.

  • T – [in]

    T is REAL array, dimension (LDT,K)

    The triangular K-by-K matrix T in the representation of the block reflector.

  • LDT – [in]

    LDT is INTEGER

    The leading dimension of the array T. LDT >= K.

  • C – [inout]

    C is REAL 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.

  • LDC – [in]

    LDC is INTEGER

    The leading dimension of the array C. LDC >= fla_max(1,M).

  • WORK – [out] WORK is REAL array, dimension (LDWORK,K)

  • LDWORK – [in]

    LDWORK is INTEGER

    The leading dimension of the array WORK.

    If SIDE = ‘L’, LDWORK >= fla_max(1,N);

    if SIDE = ‘R’, LDWORK >= fla_max(1,M).