BLAS/SRC/drotmg.f(3)

📦
version 3.12.1 · 4 versions
, in arch rolling

💖 NAME 💖

Okay so this is the page for BLAS/SRC/drotmg.f, and it comes from the Library Functions Manual. The whole vibe is DROTMG: a subroutine that's here to construct a modified Givens transformation matrix. Iconic behavior, honestly. ✨

✨ SYNOPSIS ✨

Functions/Subroutines

subroutine drotmg (dd1, dd2, dx1, dy1, dparam)
    DROTMG

🎀 Function/Subroutine Documentation 🎀

Bestie, here's the full signature so you know exactly what you're working with:

subroutine drotmg (double precision dd1, double precision dd2, double
       precision dx1, double precision dy1, double precision, dimension(5)
       dparam)
       DROTMG

🌸 Purpose 🌸

The purpose block is doing matrix main-character energy, so I'm giving it to you exactly as written — no edits, no vibes-based reinterpretation:

!>
!>    CONSTRUCT THE MODIFIED GIVENS TRANSFORMATION MATRIX H WHICH ZEROS
!>    THE SECOND COMPONENT OF THE 2-VECTOR  (DSQRT(DD1)*DX1,DSQRT(DD2)*>    DY2)**T.
!>    WITH DPARAM(1)=DFLAG, H HAS ONE OF THE FOLLOWING FORMS..
!>
!>    DFLAG=-1.D0     DFLAG=0.D0        DFLAG=1.D0     DFLAG=-2.D0
!>
!>      (DH11  DH12)    (1.D0  DH12)    (DH11  1.D0)    (1.D0  0.D0)
!>    H=(          )    (          )    (          )    (          )
!>      (DH21  DH22),   (DH21  1.D0),   (-1.D0 DH22),   (0.D0  1.D0).
!>    LOCATIONS 2-4 OF DPARAM CONTAIN DH11, DH21, DH12, AND DH22
!>    RESPECTIVELY. (VALUES OF 1.D0, -1.D0, OR 0.D0 IMPLIED BY THE
!>    VALUE OF DPARAM(1) ARE NOT STORED IN DPARAM.)
!>
!>    THE VALUES OF GAMSQ AND RGAMSQ SET IN THE DATA STATEMENT MAY BE
!>    INEXACT.  THIS IS OK AS THEY ARE ONLY USED FOR TESTING THE SIZE
!>    OF DD1 AND DD2.  ALL ACTUAL SCALING OF DATA IS DONE USING GAM.
!>
!>

So basically: it constructs the modified Givens transformation matrix H that zeros the second component of that 2-vector. With DPARAM(1)=DFLAG, H has one of the four forms shown above. Locations 2-4 of DPARAM contain DH11, DH21, DH12, and DH22 respectively. The 1.D0, -1.D0, or 0.D0 values implied by DPARAM(1) are not stored in DPARAM. 🫶

⚠️ Caveat alert: GAMSQ and RGAMSQ set in the data statement may be inexact. That's fine because they're only used for testing the size of DD1 and DD2. All actual scaling of data is done using GAM. Periodt. 💅

💜 Parameters 💜

  • DD1 — DD1 is DOUBLE PRECISION. 🌸
  • DD2 — DD2 is DOUBLE PRECISION. 🎀
  • DX1 — DX1 is DOUBLE PRECISION. 🦋
  • DY1 — DY1 is DOUBLE PRECISION. 🌈
  • DPARAM — DPARAM is DOUBLE PRECISION array, dimension (5). 💖
DPARAM(1)=DFLAG
DPARAM(2)=DH11
DPARAM(3)=DH21
DPARAM(4)=DH12
DPARAM(5)=DH22

👑 Author 👑

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

Definition at line 89 of file drotmg.f. 🫶

🌈 Author 🌈

Generated automatically by Doxygen for LAPACK from the source code. 💖

That's the whole page, bestie! This one is from LAPACK, Version 3.12.0, and the page is BLAS/SRC/drotmg.f(3). Go off, linear algebra icon 👑💖

📦 where this page comes from