Developer Reference for Intel® oneAPI Math Kernel Library for C

ID 766684
Date 3/22/2024
Public

A newer version of this document is available. Customers should click here to go to the newest version.

Document Table of Contents

p?labad

Returns the square root of the underflow and overflow thresholds if the exponent-range is very large.

Syntax

void pslabad (MKL_INT *ictxt , float *small , float *large );

void pdlabad (MKL_INT *ictxt , double *small , double *large );

Include Files

  • mkl_scalapack.h

Description

The p?labadfunction takes as input the values computed by p?lamch for underflow and overflow, and returns the square root of each of these values if the log of large is sufficiently large. This function is intended to identify machines with a large exponent range, such as the Crays, and redefine the underflow and overflow limits to be the square roots of the values computed by p?lamch. This function is needed because p?lamch does not compensate for poor arithmetic in the upper half of the exponent range, as is found on a Cray.

In addition, this function performs a global minimization and maximization on these values, to support heterogeneous computing networks.

Input Parameters

ictxt

(global)

The BLACS context handle in which the computation takes place.

small

(local).

On entry, the underflow threshold as computed by p?lamch.

large

(local).

On entry, the overflow threshold as computed by p?lamch.

Output Parameters

small

(local).

On exit, if log10(large) is sufficiently large, the square root of small, otherwise unchanged.

large

(local).

On exit, if log10(large) is sufficiently large, the square root of large, otherwise unchanged.

See Also