SSLECT(3)

📦 version 3.12.0, in opensuse-leap 16.0

🌸 SSLECT(3) — the eigenvalue vibe-checker 💅

ok so real talk, this page is from the Library Functions Manual, and the file it's documenting is literally:

/home/abui...IG/sslect.f(3)

it's shorter than my attention span after 11pm and honestly? iconic for that. let's get into it 🫶

✨ NAME ✨

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/TESTING/EIG/sslect.f

yep. that's the whole name. she's a whole path and she owns it 👑

🦋 SYNOPSIS 🦋

Functions/Subroutines

  • logical function SSLECT (zr, zi) — SSLECT

that's it, that's the synopsis, we love a minimal queen ✨

💖 Function/Subroutine Documentation 💖

logical function SSLECT (real zr, real zi)

SSLECT

🎀 Purpose 🎀

!>
!> SSLECT returns .TRUE. if the eigenvalue ZR+sqrt(-1)*ZI is to be
!> selected, and otherwise it returns .FALSE.
!> It is used by SCHK41 to test if SGEES successfully sorts eigenvalues,
!> and by SCHK43 to test if SGEESX successfully sorts eigenvalues.
!>
!> The common block /SSLCT/ controls how eigenvalues are selected.
!> If SELOPT = 0, then SSLECT return .TRUE. when ZR is less than zero,
!> and .FALSE. otherwise.
!> If SELOPT is at least 1, SSLECT returns SELVAL(SELOPT) and adds 1
!> to SELOPT, cycling back to 1 at SELMAX.
!>

ok so picture this bestie: SSLECT is basically the bouncer at the eigenvalue club 🚪✨ she looks at a complex eigenvalue ZR+sqrt(-1)*ZI and is like ".TRUE., you're on the list" or ".FALSE., not tonight babes." no cap.

who's she working for? two whole test routines, fr fr:

  • SCHK41 — she helps it check whether SGEES actually sorts eigenvalues correctly 😤
  • SCHK43 — same deal, but for SGEESX 🔥

and the actual guest list rules live in the common block /SSLCT/. so how does she decide? two modes, and they are not the same vibe:

  • if SELOPT = 0, she returns .TRUE. when ZR is less than zero, and .FALSE. otherwise 🙈
  • if SELOPT is at least 1, she returns SELVAL(SELOPT) and adds 1 to SELOPT, cycling back to 1 at SELMAX 🌀 (yes she loops, yes she's extra, we stan a rotating roster)
⚠️ heads up: those two branches behave completely differently depending on SELOPT. she is not doing the same thing twice with a cute outfit change — it's a real mode switch, so know which one you're in 💀

🌈 Parameters 🌈

  • ZR — !> ZR is REAL and !> The real part of a complex eigenvalue ZR + i*ZI. so like, the real one 💜
  • ZI — !> ZI is REAL and !> The imaginary part of a complex eigenvalue ZR + i*ZI. the imaginary bestie 🦋

👑 Author 👑

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

four whole institutions on the credits, main character energy honestly 🌟

⭐ Definition ⭐

Definition at line 61 of file sslect.f.

line 61, screenshot it 📸

💫 Author 💫

Generated automatically by Doxygen for LAPACK from the source code.

so nobody hand-wrote this, a robot did it, and honestly the robot ate 🤖💅

LAPACK — Version 3.12.0 — /home/abui...IG/sslect.f(3)

k that's the whole page bestie, go sort some eigenvalues, ily, bye 🎀✨💖

📦 where this page comes from