..
  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.
  =====================================================================
     .. Local Scalars ..