SRC/dlaed5.f(3)

📦
version 3.12.1 · 7 versions
, in arch rolling

🌸 NAME 🌸

SRC/dlaed5.f — this is the Library Functions Manual page for SRC/dlaed5.f(3), and bestie, it’s giving tiny Fortran subroutine with main character energy 💅

✨ SYNOPSIS ✨

Functions/Subroutines

subroutine dlaed5 (i, d, z, delta, rho, dlam)

DLAED5 used by DSTEDC. Solves the 2-by-2 secular equation.

🎀 Function/Subroutine Documentation 🎀

subroutine dlaed5 (integer i, double precision, dimension( 2 ) d, double
       precision, dimension( 2 ) z, double precision, dimension( 2 ) delta,
       double precision rho, double precision dlam)

DLAED5 used by DSTEDC. Solves the 2-by-2 secular equation.

🦋 Purpose 🦋

okay so this subroutine computes the I-th eigenvalue of a symmetric rank-one modification of a 2-by-2 diagonal matrix, and the matrix is literally:

diag( D )  +  RHO * Z * transpose(Z) .

The diagonal elements in the array D are assumed to satisfy:

D(i) < D(j)  for  i < j .

We also assume RHO > 0 and that the Euclidean norm of the vector Z is one. That’s the vibe check for the math, periodt ✨

🍓 Parameters 🍓

  • I — I is INTEGER. The index of the eigenvalue to be computed. I = 1 or I = 2.
  • D — D is DOUBLE PRECISION array, dimension (2). The original eigenvalues. We assume D(1) < D(2).
  • Z — Z is DOUBLE PRECISION array, dimension (2). The components of the updating vector.
  • DELTA — DELTA is DOUBLE PRECISION array, dimension (2). The vector DELTA contains the information necessary to construct the eigenvectors.
  • RHO — RHO is DOUBLE PRECISION. The scalar in the symmetric updating formula.
  • DLAM — DLAM is DOUBLE PRECISION. The computed lambda_I, the I-th updated eigenvalue.

👑 Author 👑

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

🌈 Contributors 🌈

  • Ren-Cang Li, Computer Science Division, University of California at Berkeley, USA

Definition at line 107 of file dlaed5.f. 🫶

👑 Author 👑

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mwah 💖 that’s the whole page: LAPACK Version 3.12.0, sourced from SRC/dlaed5.f(3). bye bestie 🫶

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