man pdlamch (Fonctions bibliothèques) - determine double precision machine parameters

NAME

PDLAMCH - determine double precision machine parameters

PDLAMCH determines double precision machine parameters.

ICTXT (global input) INTEGER: The BLACS context handle in which the computation takes place.
CMACH (global input) CHARACTER*1: Specifies the value to be returned by PDLAMCH:

= 'E' or 'e', PDLAMCH := eps

= 'S' or 's , PDLAMCH := sfmin

= 'B' or 'b', PDLAMCH := base

= 'P' or 'p', PDLAMCH := eps*base

= 'N' or 'n', PDLAMCH := t

= 'R' or 'r', PDLAMCH := rnd

= 'M' or 'm', PDLAMCH := emin

= 'U' or 'u', PDLAMCH := rmin

= 'L' or 'l', PDLAMCH := emax

= 'O' or 'o', PDLAMCH := rmax

where

eps = relative machine precision: sfmin = safe minimum, such that 1/sfmin does not overflow base = base of the machine prec = eps*base t = number of (base) digits in the mantissa rnd = 1.0 when rounding occurs in addition, 0.0 otherwise emin = minimum exponent before (gradual) underflow rmin = underflow threshold - base**(emin-1) emax = largest exponent before overflow rmax = overflow threshold - (base**emax)*(1-eps)