DLARRR(3)

💖 DLARRR(3) — the tridiagonal accuracy vibe check 💖

okay bestie, this is the DLARRR(3) page from the Library Functions Manual. It’s lowkey a Fortran subroutine that does a vibe check on a symmetric tridiagonal matrix T before anyone spends expensive compute on the eigenvalues. No cap.

✨ NAME ✨

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/dlarrr.f

🌸 SYNOPSIS 🌸

Functions/Subroutines

• subroutine DLARRR (n, d, e, info) — DLARRR runs tests to decide whether the symmetric tridiagonal matrix T actually warrants those expensive computations that guarantee high relative accuracy in the eigenvalues. It’s giving gatekeeper, but make it numerical.

🦋 Function/Subroutine Documentation 🦋

subroutine DLARRR (integer n, double precision, dimension( * ) d, double precision, dimension( * ) e, integer info)

The subroutine runs tests to decide whether the symmetric tridiagonal matrix T warrants expensive computations which guarantee high relative accuracy in the eigenvalues. That’s the whole assignment, and she ate.

🎀 Purpose 🎀

The purpose here is to run tests that decide whether the symmetric tridiagonal matrix T warrants expensive computations which guarantee high relative accuracy in the eigenvalues. Basically: should we go all-out for high relative accuracy, or is absolute accuracy enough? The subroutine is the friend who checks before you book the whole group trip.

💅 Parameters 💅

N

• N is INTEGER.
• The order of the matrix. N > 0. Periodt.

D

• D is DOUBLE PRECISION array, dimension (N).
• The N diagonal elements of the tridiagonal matrix T.

E

• E is DOUBLE PRECISION array, dimension (N).
• On entry, the first (N-1) entries contain the subdiagonal elements of the tridiagonal matrix T; E(N) is set to ZERO.

INFO

• INFO is INTEGER.
• INFO = 0(default) : the matrix warrants computations preserving relative accuracy.
• INFO = 1 : the matrix warrants computations guaranteeing only absolute accuracy.

👑 Author 👑

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

🌈 Contributors 🌈

• Beresford Parlett, University of California, Berkeley, USA
• Jim Demmel, University of California, Berkeley, USA
• Inderjit Dhillon, University of Texas, Austin, USA
• Osni Marques, LBNL/NERSC, USA
• Christof Voemel, University of California, Berkeley, USA

🍓 Definition at line 93 of file dlarrr.f. 🍓

Definition at line 93 of file dlarrr.f.

🧚 Author (auto-generated Doxygen edition) 🧚

Generated automatically by Doxygen for LAPACK from the source code.

---

okay that’s the whole page, bestie! footer sign-off: source/version is LAPACK Version 3.12.0, path vibes /home/abui...RC/dlarrr.f(3), and there’s no date shown on the page, so we’re not inventing one. slay 💜