SRC/dlarra.f(3)

💖 NAME 💖

okay so this page is SRC/dlarra.f(3) from the Library Functions Manual, and the actual file we're hyping is SRC/dlarra.f — main character energy, no cap. 💅

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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 🦋

Here's the full signature, bestie — copy it exactly because we do not freestyle API types:

   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. ✨

💡 Purpose 💡

okay so what does it actually do? Compute the splitting points with threshold SPLTOL. DLARRA sets any off-diagonal elements to zero. That's the whole vibe. 💖

🎀 Parameters 🎀

• N — N is INTEGER. The order of the matrix. N > 0.
• D — D is DOUBLE PRECISION array, dimension (N). On entry, 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) need not be set. On exit, the entries E( ISPLIT( I ) ), 1 <= I <= NSPLIT, are set to zero, the other entries of E are untouched.
• 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.
• SPLTOL — SPLTOL is DOUBLE PRECISION. 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. The norm of the matrix.
• NSPLIT — NSPLIT is INTEGER. The number of blocks T splits into. 1 <= NSPLIT <= N.
• ISPLIT — ISPLIT is INTEGER array, dimension (N). 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.
• INFO — INFO is INTEGER. = 0: successful exit.

👑 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. 📍

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👑 Author (generated edition) 👑

Generated automatically by Doxygen for LAPACK from the source code. 🤖💖

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mwah 💋 — this page is LAPACK Version 3.12.0, source SRC/dlarra.f(3). The footer doesn't list a date, so no cap, no invented date. 🫶