DLARRA(3)

💖 DLARRA(3) 💖

okay bestie, welcome to the Library Functions Manual — this page is for the LAPACK subroutine DLARRA, and it's giving “find the splitting points” main character energy. No cap, here's the whole vibe. 🦋

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💅 NAME 💅

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

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✨ SYNOPSIS ✨

Functions/Subroutines

subroutine DLARRA (n, d, e, e2, spltol, tnrm, nsplit, isplit, info)
    DLARRA computes the splitting points with the specified threshold.

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🦋 Function/Subroutine Documentation 🦋

subroutine DLARRA (integer n, double precision, dimension( * ) d, double precision, dimension( * ) e, double precision, dimension( * ) e2, double precision spltol, double precision tnrm, integer nsplit, integer, dimension( * ) isplit, integer info)

DLARRA computes the splitting points with the specified threshold. That's the whole assignment, and she ate. 💅

🎀 Purpose 🎀

!>
!> Compute the splitting points with threshold SPLTOL.
!> DLARRA sets any  off-diagonal elements to zero.
!>

🍓 Parameters 🍓

🔢 N

N is INTEGER. It's the order of the matrix, and the vibe check is N > 0. Periodt.

🔢 D

D is DOUBLE PRECISION array, dimension (N). On entry, it's the N diagonal elements of the tridiagonal matrix T. Main character diagonal, fr fr.

🔢 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) need not be set.

On exit, the entries E( ISPLIT( I ) ), 1 <= I <= NSPLIT, are set to zero, and the other entries of E are untouched. Obsessed with a clean little update. ✨

🔢 E2

E2 is DOUBLE PRECISION array, dimension (N). On entry, the first (N-1) entries contain the SQUARES of the subdiagonal elements of the tridiagonal matrix T; E2(N) need not be set.

On exit, the entries E2( ISPLIT( I ) ), 1 <= I <= NSPLIT, have been set to zero. That's the squared-up glow-down, bestie. 🫶

🔢 SPLTOL

SPLTOL is DOUBLE PRECISION. It's the threshold for splitting. Two criteria can be used:

• SPLTOL<0 : criterion based on absolute off-diagonal value
• SPLTOL>0 : criterion that preserves relative accuracy

🔢 TNRM

TNRM is DOUBLE PRECISION. It's the norm of the matrix. That's the flex. 💅

🔢 NSPLIT

NSPLIT is INTEGER. It's the number of blocks T splits into. Constraint vibe: 1 <= NSPLIT <= N.

🔢 ISPLIT

ISPLIT is INTEGER array, dimension (N). It's the splitting points, at which T breaks up into blocks.

The first block consists of rows/columns 1 to ISPLIT(1), the second of rows/columns ISPLIT(1)+1 through ISPLIT(2), etc., and the NSPLIT-th consists of rows/columns ISPLIT(NSPLIT-1)+1 through ISPLIT(NSPLIT)=N. Okay that's a lot of numbers but it's iconic. 🎀

🔢 INFO

INFO is INTEGER. Here, = 0 means successful exit. Slay. 🔥

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👑 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 134 of file dlarra.f.

🤖 Author 🤖

Generated automatically by Doxygen for LAPACK from the source code.

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okay bye bestie 💜 — signing off from the footer: LAPACK Version 3.12.0, page /home/abui...RC/dlarra.f(3). That's the whole vibe, no cap. 🫶