lis_array_qr(3)

📦 version 2.1.11, in fedora 43, fedora 44, nixos 26.05, nixpkgs unstable

✨ lis_array_qr(3) — it's giving "eigenvalues, but make it QR" ✨

okay bestie, so this is a page from the Lis Library Functions manual, section 3, and it's literally all about lis_array_qr. pull up a chair, grab a boba 🧋, and let's get into it.

💖 NAME 💖

lis_array_qr — calculate the eigenvalues with the QR algorithm

🦋 SYNOPSIS 🦋

#include "lis.h"

LIS_INT lis_array_qr(LIS_INT n, LIS_SCALAR a[], LIS_SCALAR q[],
LIS_SCALAR r[], LIS_INT *qriter, LIS_SCALAR *qrerr);

🌸 DESCRIPTION 🌸

so basically?? you hand it matrix A and it goes and calculates the eigenvalues of matrix A with the QR algorithm. that's the whole vibe. it ate, no crumbs. 💅

🎀 INPUT 🎀

the stuff you gotta bring to the function:

  • n — the size of the matrices, bestie. the actual dimensions.
  • a — the array that stores matrix A of size n * n. this is the main character right here 👑
  • q — the work array Q of size n * n. it's a work array, it's doing the labor, respect it 🙏
  • r — the work array R of size n * n. also clocking in for work-array duty.

⭐ OUTPUT ⭐

what you get back after the glow-up:

  • a — the array that stores the block upper-triangular matrix with eigenvalues in the block diagonal elements after similarity transformation. like, it literally got transformed, and the eigenvalues are chilling in the block diagonal elements. iconic behavior. ✨
  • qriter — the number of iterations of the QR algorithm. counting every single one, no skips 🫶
  • qrerr — the 2-norm of the first subdiagonal element A(2,1) after similarity transformation. yes, that specific one. it's giving very precise. 💀

🌈 EXIT STATUS 🌈

the following exit values are returned, and you WILL be checking them:

  • 0 — the process is normally terminated. slay, everything went perfect, go off queen 🎉
  • unspecified — an error occurred. not slay. something went wrong, and the docs are just like "unspecified" about it 😭

🍓 SEE ALSO 🍓

fr fr, that URL is the whole LIS mothership — go peek if you wanna know more. 🛸

okay that's the whole page, bestie!! this was the lis_array_qr(3) man page from 1 Nov 2014, and it lives under the big lis umbrella of Lis Library Functions. mwah, love you, go compute some eigenvalues 💖✨🦋

📦 where this page comes from