TESTING/LIN/xlaenv.f(3)

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version 3.12.1 · 2 versions
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NAME

TESTING/LIN/xlaenv.f — bestie, this is the page for that file, straight out of the Library Functions Manual 💅. It’s giving “tiny subroutine, very important tuning-knob energy” ✨.

SYNOPSIS

Functions/Subroutines

subroutine xlaenv (ispec, nvalue)
    XLAENV

Function/Subroutine Documentation

subroutine xlaenv (integer ispec, integer nvalue)

XLAENV 👑 — the subroutine itself, no cap.

Purpose:

Okay so XLAENV sets certain machine- and problem-dependent quantities which will later be retrieved by ILAENV. That’s the whole job, and it ate 🔥.

Parameters

ISPEC

ISPEC is INTEGER 🫶. It specifies the parameter to be set in the COMMON array IPARMS.

  • = 1 — the optimal blocksize; if this value is 1, an unblocked algorithm will give the best performance.
  • = 2 — the minimum block size for which the block routine should be used; if the usable block size is less than this value, an unblocked routine should be used.
  • = 3 — the crossover point (in a block routine, for N less than this value, an unblocked routine should be used).
  • = 4 — the number of shifts, used in the nonsymmetric eigenvalue routines.
  • = 5 — the minimum column dimension for blocking to be used; rectangular blocks must have dimension at least k by m, where k is given by ILAENV(2,...) and m by ILAENV(5,...).
  • = 6 — the crossover point for the SVD (when reducing an m by n matrix to bidiagonal form, if max(m,n)/min(m,n) exceeds this value, a QR factorization is used first to reduce the matrix to a triangular form).
  • = 7 — the number of processors.
  • = 8 — another crossover point, for the multishift QR and QZ methods for nonsymmetric eigenvalue problems.
  • = 9 — maximum size of the subproblems at the bottom of the computation tree in the divide-and-conquer algorithm (used by xGELSD and xGESDD).
  • =10 — ieee NaN arithmetic can be trusted not to trap.
  • =11 — infinity arithmetic can be trusted not to trap.

NVALUE

NVALUE is INTEGER 🌸. It’s the value of the parameter specified by ISPEC. Simple, iconic, periodt.

Author

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

Definition at line 77 of file xlaenv.f.

Author 💖 (auto-generated note)

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