NAME¶
PDLABAD - take as input the values computed by PDLAMCH for underflow and
overflow, and returns the square root of each of these values if the log of
LARGE is sufficiently large
SYNOPSIS¶
- SUBROUTINE PDLABAD(
- ICTXT, SMALL, LARGE )
INTEGER ICTXT DOUBLE PRECISION LARGE, SMALL
PURPOSE¶
PDLABAD takes as input the values computed by PDLAMCH 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 PDLAMCH. This
subroutine is needed because PDLAMCH 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) DOUBLE PRECISION
- On entry, the underflow threshold as computed by PDLAMCH. On exit, if
LOG10(LARGE) is sufficiently large, the square root of SMALL, otherwise
unchanged.
- LARGE (local input/local output) DOUBLE PRECISION
- On entry, the overflow threshold as computed by PDLAMCH. On exit, if
LOG10(LARGE) is sufficiently large, the square root of LARGE, otherwise
unchanged.
