pdlamch3

Purpose

PDLAMCH determines double precision machine parameters.

Arguments

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)