slabad.f

Go to the documentation of this file.

      SUBROUTINE slabad( SMALL, LARGE )
*
*  -- LAPACK auxiliary routine (version 3.2) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     .. Scalar Arguments ..
      REAL               large, small
*     ..
*
*  Purpose
*  =======
*
*  SLABAD takes as input the values computed by SLAMCH 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 SLAMCH.  This subroutine is needed because
*  SLAMCH does not compensate for poor arithmetic in the upper half of
*  the exponent range, as is found on a Cray.
*
*  Arguments
*  =========
*
*  SMALL   (input/output) REAL
*          On entry, the underflow threshold as computed by SLAMCH.
*          On exit, if LOG10(LARGE) is sufficiently large, the square
*          root of SMALL, otherwise unchanged.
*
*  LARGE   (input/output) REAL
*          On entry, the overflow threshold as computed by SLAMCH.
*          On exit, if LOG10(LARGE) is sufficiently large, the square
*          root of LARGE, otherwise unchanged.
*
*  =====================================================================
*
*     .. 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
*
      return
*
*     End of SLABAD
*
      END