SUBROUTINE PSLABAD( ICTXT, SMALL, LARGE )
*
* -- ScaLAPACK auxiliary routine (version 1.5) --
* University of Tennessee, Knoxville, Oak Ridge National Laboratory,
* and University of California, Berkeley.
* May 1, 1997
*
* .. Scalar Arguments ..
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.
*
* =====================================================================
*
* .. Local Scalars ..
INTEGER IDUMM
* ..
* .. External Subroutines ..
EXTERNAL SGAMN2D, SGAMX2D
* ..
* .. Intrinsic Functions ..
INTRINSIC LOG10, SQRT
* ..
* .. Executable Statements ..
*
* If it looks like we're on a Cray, take the square root of
* SMALL and LARGE to avoid overflow and underflow problems.
*
IF( LOG10( LARGE ).GT.2000. ) THEN
SMALL = SQRT( SMALL )
LARGE = SQRT( LARGE )
END IF
*
CALL SGAMX2D( ICTXT, 'All', ' ', 1, 1, SMALL, 1, IDUMM,
$ IDUMM, -1, -1, IDUMM )
CALL SGAMN2D( ICTXT, 'All', ' ', 1, 1, LARGE, 1, IDUMM,
$ IDUMM, -1, -1, IDUMM )
*
RETURN
*
* End of PSLABAD
*
END