/home/abui...C/drotmg.f(3)

🌸 NAME 🌸

okay bestie, so this page is from the Library Functions Manual and it's literally all about /home/abui...C/drotmg.f(3) — yes, that whole long path is the name, don't @ me 💅. It's the manpage for the Fortran subroutine DROTMG, and she's iconic for constructing modified Givens rotations. periodt.

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✨ SYNOPSIS ✨

here's the whole vibe in one code block, no cap:

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

and yes, the subroutine is literally named DROTMG — she said "I'll have my name in the title and in the body, twice" 👑

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🎀 Function/Subroutine Documentation 🎀

💖 subroutine DROTMG 💖

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

🧚 Purpose 🧚

okay so the whole point, fr fr, is to 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… and the way these matrices are formatted is giving linear algebra couture:

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.) 🙈

⚠️ also bestie, 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 like, don't panic, it's fine 💀

🌈 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

like, every single one is double precision and every single location in DPARAM is accounted for. organized queen 👑

👑 Author 👑

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

definition at line 89 of file drotmg.f. ✨

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👑 Author 👑

generated automatically by Doxygen for LAPACK from the source code. (yes, this is a second Author section, she's extra like that 💅)

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🫶 and that's the whole page bestie! LAPACK Version 3.12.0, source file /home/abui...C/drotmg.f(3) — go forth and rotate those Givens, ily! 💖✨