SRC/ilaenv2stage.f(3)

🌸 SRC/ilaenv2stage.f 🌸

Okay bestie, welcome to the SRC/ilaenv2stage.f page from the LAPACK Library Functions Manual — yes, we are deep in Fortran oracle territory and it is lowkey iconic.

✨ NAME ✨

SRC/ilaenv2stage.f — that is the page/file in question, and it is giving “I contain the tuning-parameter lore” energy.

✨ SYNOPSIS ✨

Functions/Subroutines

integer function ilaenv2stage (ispec, name, opts, n1, n2, n3, n4)
    ILAENV2STAGE

📚 Function/Subroutine Documentation 📚

integer function ilaenv2stage (integer ispec, character*( * ) name,
    character*( * ) opts, integer n1, integer n2, integer n3, integer n4)
    ILAENV2STAGE

🎯 Purpose 🎯

ILAENV2STAGE is called from the LAPACK routines to choose problem-dependent parameters for the local environment. See ISPEC for a description of the parameters.

It sets problem and machine dependent parameters useful for *_2STAGE and related subroutines.

ILAENV2STAGE returns an INTEGER.

• if ILAENV2STAGE >= 0: ILAENV2STAGE returns the value of the parameter specified by ISPEC.
• if ILAENV2STAGE < 0: if ILAENV2STAGE = -k, the k-th argument had an illegal value.

This version provides a set of parameters which should give good, but not optimal, performance on many of the currently available computers for the 2-stage solvers. Users are encouraged to modify this subroutine to set the tuning parameters for their particular machine using the option and problem size information in the arguments.

⚠️ This routine will not function correctly if it is converted to all lower case. Converting it to all upper case is allowed.

🧚 Parameters 🧚

ISPEC

ISPEC is INTEGER. It specifies the parameter to be returned as the value of ILAENV2STAGE.

• = 1: the optimal blocksize nb for the reduction to BAND
• = 2: the optimal blocksize ib for the eigenvectors singular vectors update routine
• = 3: The length of the array that store the Housholder representation for the second stage Band to Tridiagonal or Bidiagonal
• = 4: The workspace needed for the routine in input.
• = 5: For future release.

NAME

NAME is CHARACTER*(*). It is the name of the calling subroutine, in either upper case or lower case.

OPTS

OPTS is CHARACTER*(*). These are the character options to the subroutine NAME, concatenated into a single character string. For example, UPLO = 'U', TRANS = 'T', and DIAG = 'N' for a triangular routine would be specified as OPTS = 'UTN'.

N1

N1 is INTEGER.

N2

N2 is INTEGER.

N3

N3 is INTEGER.

N4

N4 is INTEGER. Problem dimensions for the subroutine NAME; these may not all be required.

🫶 Author 🫶

• Univ. of Tennessee
• Univ. of California Berkeley
• Univ. of Colorado Denver
• NAG Ltd.
• Nick R. Papior

🔍 Further Details 🔍

The following conventions have been used when calling ILAENV2STAGE from the LAPACK routines:

1. OPTS is a concatenation of all of the character options to subroutine NAME, in the same order that they appear in the argument list for NAME, even if they are not used in determining the value of the parameter specified by ISPEC.
2. The problem dimensions N1, N2, N3, N4 are specified in the order that they appear in the argument list for NAME. N1 is used first, N2 second, and so on, and unused problem dimensions are passed a value of -1.
3. The parameter value returned by ILAENV2STAGE is checked for validity in the calling subroutine.

📍 Definition at line 148 of file ilaenv2stage.f.

🎀 Author 🎀

Generated automatically by Doxygen for LAPACK from the source code.

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Bye bestie 💖 — this page is from LAPACK, version 3.12.0, and its source/page tag is SRC/ilaenv2stage.f(3). Slay, no cap. 🌈👑