CGEMQR(3)

🎀 NAME 🎀

okay bestie, this is the cgemqr.f(3) page from the Library Functions Manual, and the file it’s serving is:

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/cgemqr.f

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✨ SYNOPSIS ✨

🦋 Functions/Subroutines 🦋

subroutine CGEMQR (side, trans, m, n, k, a, lda, t, tsize, c, ldc, work,
    lwork, info)

CGEMQR

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💖 Function/Subroutine Documentation 💖

🫶 CGEMQR 🫶

subroutine CGEMQR (character side, character trans, integer m, integer n,
    integer k, complex, dimension( lda, * ) a, integer lda, complex,
    dimension( * ) t, integer tsize, complex, dimension( ldc, * ) c, integer
    ldc, complex, dimension( * ) work, integer lwork, integer info)

CGEMQR

🌸 Purpose 🌸

okay so here’s the actual vibe of what this routine does — it overwrites the general real M-by-N matrix C with:

!>
!> CGEMQR overwrites the general real M-by-N matrix C with
!>
!>                      SIDE = 'L'     SIDE = 'R'
!>      TRANS = 'N':      Q * C          C * Q
!>      TRANS = 'T':      Q**H * C       C * Q**H
!>
!> where Q is a complex unitary matrix defined as the product
!> of blocked elementary reflectors computed by tall skinny
!> QR factorization (CGEQR)
!>
!>

so yeah, Q is the complex unitary main character, built from the product of blocked elementary reflectors from tall skinny QR factorization (CGEQR). slay.

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💅 Parameters 💅

• SIDE — SIDE is CHARACTER*1. It’s the side-picker:
  • = 'L': apply Q or Q**H from the Left;
  • = 'R': apply Q or Q**H from the Right.
• TRANS — TRANS is CHARACTER*1. This tells it whether we’re transposing or not:
  • = 'N': No transpose, apply Q;
  • = 'C': Conjugate transpose, apply Q**H.
• M — M is INTEGER. The number of rows of the matrix A. M >=0.
• N — N is INTEGER. The number of columns of the matrix C. N >= 0.
• K — K is INTEGER. The number of elementary reflectors whose product defines the matrix Q.
  • If SIDE = 'L', M >= K >= 0;
  • if SIDE = 'R', N >= K >= 0.
• A — A is COMPLEX array, dimension (LDA,K). Part of the data structure to represent Q as returned by CGEQR.
• LDA — LDA is INTEGER. The leading dimension of the array A.
  • If SIDE = 'L', LDA >= max(1,M);
  • if SIDE = 'R', LDA >= max(1,N).
• T — T is COMPLEX array, dimension (MAX(5,TSIZE)). Part of the data structure to represent Q as returned by CGEQR.
• TSIZE — TSIZE is INTEGER. The dimension of the array T. TSIZE >= 5.
• C — C is COMPLEX array, dimension (LDC,N).
  • On entry, the M-by-N matrix C.
  • On exit, C is overwritten by Q*C or Q**H*C or C*Q**H or C*Q.
• LDC — LDC is INTEGER. The leading dimension of the array C. LDC >= max(1,M).
• WORK — (workspace) COMPLEX array, dimension (MAX(1,LWORK)).
• LWORK — LWORK is INTEGER. The dimension of the array WORK.
  • If LWORK = -1, then a workspace query is assumed. The routine only calculates the size of the WORK array, returns this value as WORK(1), and no error message related to WORK is issued by XERBLA.
• INFO — INFO is INTEGER:
  • = 0: successful exit
  • < 0: if INFO = -i, the i-th argument had an illegal value

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👑 Author 👑

• Univ. of Tennessee
• Univ. of California Berkeley
• Univ. of Colorado Denver
• NAG Ltd.

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🔥 Further Details 🔥

These details are particular for this LAPACK implementation. Users should not take them for granted. These details may change in the future, and are not likely true for another LAPACK implementation. These details are relevant if one wants to try to understand the code. They are not part of the interface.

In this version,

T(2): row block size (MB)
T(3): column block size (NB)
T(6:TSIZE): data structure needed for Q, computed by
                 CLATSQR or CGEQRT

Depending on the matrix dimensions M and N, and row and column block sizes MB and NB returned by ILAENV, CGEQR will use either CLATSQR (if the matrix is tall-and-skinny) or CGEQRT to compute the QR factorization. This version of CGEMQR will use either CLAMTSQR or CGEMQRT to multiply matrix Q by another matrix. Further Details in CLAMTSQR or CGEMQRT.

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Definition at line 172 of file cgemqr.f.

🤖 Author 🤖

Generated automatically by Doxygen for LAPACK from the source code.

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okay that’s the whole page, bestie 💖 — signed off by LAPACK Version 3.12.0 and the footer path /home/abui...RC/cgemqr.f(3) (the footer doesn’t give a date, so no invented date, periodt ✨).