SYNOPSIS

SUBROUTINE PSLABAD(

ICTXT, SMALL, LARGE )

    

INTEGER ICTXT

    

REAL LARGE, SMALL

PURPOSE

PSLABAD takes as input the values computed by PSLAMCH for underflow and overflow, and returns the square root of each of these values if the log of LARGE is sufficiently large. This subroutine 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 PSLAMCH. This subroutine is needed because PSLAMCH does not compensate for poor arithmetic in the upper half of the exponent range, as is found on a Cray.

In addition, this routine performs a global minimization and maximi- zation on these values, to support heterogeneous computing networks.

ARGUMENTS

ICTXT (global input) INTEGER

The BLACS context handle in which the computation takes place.

SMALL (local input/local output) REAL

On entry, the underflow threshold as computed by PSLAMCH. On exit, if LOG10(LARGE) is sufficiently large, the square root of SMALL, otherwise unchanged.

LARGE (local input/local output) REAL

On entry, the overflow threshold as computed by PSLAMCH. On exit, if LOG10(LARGE) is sufficiently large, the square root of LARGE, otherwise unchanged.