SRC/cgemqr.f(3)

📦
version 3.12.1 · 4 versions
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💅 SRC/cgemqr.f

ok so this is a page from the Library Functions Manual, bestie — it's the CGEMQR story and it's honestly a whole vibe ✨

🌸 NAME 🌸

SRC/cgemqr.f — that's the file, that's the name, periodt 💅

🎀 SYNOPSIS 🎀

Functions/Subroutines

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

CGEMQR 🦋

✨ Function/Subroutine Documentation ✨

Here's the full signature, copied exactly so you can screenshot it and send it to the group chat:

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 listen: CGEMQR overwrites the general real M-by-N matrix C with — and here's the little table of who-gets-multiplied-by-whom:

                     SIDE = 'L'     SIDE = 'R'
     TRANS = 'N':      Q * C          C * Q
     TRANS = 'T':      Q**H * C       C * Q**H

and where Q is a complex unitary matrix defined as the product of blocked elementary reflectors computed by tall skinny QR factorization (CGEQR) 💖

(the page fr fr says real M-by-N up there, no cap — I'm just reading it to you)

🌈 Parameters 🌈

  • SIDE — SIDE is CHARACTER*1. So: = 'L' means apply Q or Q**H from the Left; = 'R' means apply Q or Q**H from the Right.
  • TRANS — TRANS is CHARACTER*1. So: = 'N' means No transpose, apply Q; = 'C' means Conjugate transpose, apply Q**H.
  • M — M is INTEGER, the number of rows of the matrix A. M >=0. easy.
  • N — N is INTEGER, the number of columns of the matrix C. N >= 0. also easy bestie.
  • 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). It's part of the data structure to represent Q as returned by CGEQR. iconic.
  • 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. twins with A basically 🫶
  • TSIZE — TSIZE is INTEGER, the dimension of the array T. TSIZE >= 5. that's the rule.
  • 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. she gets replaced, that's her arc ✨
  • LDC — LDC is INTEGER, the leading dimension of the array C. LDC >= max(1,M). don't forget it 🙈
  • WORK — (workspace) COMPLEX array, dimension (MAX(1,LWORK)). On exit, if INFO = 0, WORK(1) returns the minimal LWORK.
  • LWORK — LWORK is INTEGER, the dimension of the array WORK. LWORK >= 1. 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. the shortcut, the little hack, main character energy 🎀
  • INFO — INFO is INTEGER. = 0: successful exit 🌸. < 0: if INFO = -i, the i-th argument had an illegal value 😭

👑 Author 👑

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

🔥 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.

ok so lowkey read that warning again, it matters 💅 not part of the interface, no promises, it can change on you.

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. 🦋

📌 Definition

Definition at line 173 of file cgemqr.f.

💜 Author 💜

Generated automatically by Doxygen for LAPACK from the source code.

and that's the whole page bestie, you ate it up 🍓✨

sign-off cuteness: this page is from LAPACK, Version 3.12.0, and it lives at SRC/cgemqr.f(3) — save it, cite it, love it 🎀💖🧚
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