SRC/slarra.f(3)

💖 SRC/slarra.f(3) — Library Functions Manual, but make it cute 💖

okay so bestie, this is the manual page for SRC/slarra.f, and it's all about the slarra subroutine. It computes splitting points with a specified threshold. No cap, it's giving numerical linear algebra main character energy. ✨

🌟 NAME 🌟

SRC/slarra.f

✨ SYNOPSIS ✨

Functions/Subroutines 🫶

subroutine slarra (n, d, e, e2, spltol, tnrm, nsplit, isplit, info)

SLARRA computes the splitting points with the specified threshold.

🌸 Function/Subroutine Documentation 🌸

subroutine slarra (integer n, real, dimension( * ) d, real, dimension( * )
    e, real, dimension( * ) e2, real spltol, real tnrm, integer nsplit,
    integer, dimension( * ) isplit, integer info)

SLARRA computes the splitting points with the specified threshold.

🎯 Purpose:

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

🧚 Parameters

• N — N is INTEGER. The order of the matrix. N > 0.
• D — D is REAL array, dimension (N). On entry, the N diagonal elements of the tridiagonal matrix T.
• E — E is REAL 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 REAL 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 REAL. 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 REAL. 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 slarra.f.

🤖 Author

Generated automatically by Doxygen for LAPACK from the source code.

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okay that's the whole page, bestie! The footer energy is LAPACK Version 3.12.0 on SRC/slarra.f(3) — source and version are right there, and there's no separate date line to quote, so I'm not inventing one 💀. Bye! 💖