SRC/slaqr1.f(3)

📦
version 3.12.1 · 4 versions
, in arch rolling

SRC/slaqr1.f(3) 💅

okay so this is the LAPACK Library Functions Manual page for SRC/slaqr1.f(3) — and bestie, it's a little subroutine moment with big QR-algorithm energy. ✨

💖 NAME 💖

SRC/slaqr1.f

That's it. That's the name. Iconic minimalism. 🎀

✨ SYNOPSIS ✨

🎀 Functions/Subroutines 🎀

  • subroutine slaqr1 (n, h, ldh, sr1, si1, sr2, si2, v) — SLAQR1 sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts.

🌈 Function/Subroutine Documentation 🌈

💅 subroutine slaqr1 💅

subroutine slaqr1 (integer n, real, dimension( ldh, * ) h, integer ldh, real
    sr1, real si1, real sr2, real si2, real, dimension( * ) v)

SLAQR1 sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts.

🎯 Purpose

Given a 2-by-2 or 3-by-3 matrix H, SLAQR1 sets v to a scalar multiple of the first column of the product

(*)  K = (H - (sr1 + i*si1)*I)*(H - (sr2 + i*si2)*I)

scaling to avoid overflows and most underflows. It is assumed that either

        1) sr1 = sr2 and si1 = -si2
    or
        2) si1 = si2 = 0.

This is useful for starting double implicit shift bulges in the QR algorithm. 🌀

🍓 Parameters

  • N — INTEGER. Order of the matrix H. N must be either 2 or 3.
  • H — REAL array, dimension (LDH,N). The 2-by-2 or 3-by-3 matrix H in (*).
  • LDH — INTEGER. The leading dimension of H as declared in the calling procedure. LDH >= N.
  • SR1 — REAL.
  • SI1 — REAL.
  • SR2 — REAL.
  • SI2 — REAL. The shifts in (*) (so that's SR1, SI1, SR2, and SI2, bestie).
  • V — REAL array, dimension (N). A scalar multiple of the first column of the matrix K in (*).

🫶 Author

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

🌸 Contributors:

Karen Braman and Ralph Byers, Department of Mathematics, University of Kansas, USA

📌 Definition at line 120 of file slaqr1.f.

🫶 Author 🫶

Generated automatically by Doxygen for LAPACK from the source code.

LAPACK Version 3.12.0 · SRC/slaqr1.f(3) — that's the footer, bestie 💖

📦 where this page comes from