HPL_pdlamch man page
HPL_pdlamch — determines machine-specific arithmetic constants.
double HPL_pdlamch( MPI_Comm COMM, const HPL_T_MACH CMACH );
HPL_pdlamch determines machine-specific arithmetic constants such as the relative machine precision (eps), the safe minimum(sfmin) such that 1/sfmin does not overflow, the base of the machine (base), the precision (prec), the number of (base) digits in the mantissa (t), whether rounding occurs in addition (rnd = 1.0 and 0.0 otherwise), the minimum exponent before (gradual) underflow (emin), the underflow threshold (rmin)- base**(emin-1), the largest exponent before overflow (emax), the overflow threshold (rmax) - (base**emax)*(1-eps).
- COMM (global/local input) MPI_Comm
The MPI communicator identifying the process collection.
- CMACH (global input) const HPL_T_MACH
Specifies the value to be returned by HPL_pdlamch
= HPL_MACH_EPS, HPL_pdlamch := eps (default)
= HPL_MACH_SFMIN, HPL_pdlamch := sfmin
= HPL_MACH_BASE, HPL_pdlamch := base
= HPL_MACH_PREC, HPL_pdlamch := eps*base
= HPL_MACH_MLEN, HPL_pdlamch := t
= HPL_MACH_RND, HPL_pdlamch := rnd
= HPL_MACH_EMIN, HPL_pdlamch := emin
= HPL_MACH_RMIN, HPL_pdlamch := rmin
= HPL_MACH_EMAX, HPL_pdlamch := emax
= HPL_MACH_RMAX, HPL_pdlamch := rmax
eps = relative machine precision,
sfmin = safe minimum,
base = base of the machine,
prec = eps*base,
t = number of digits in the mantissa,
rnd = 1.0 if rounding occurs in addition,
emin = minimum exponent before underflow,
rmin = underflow threshold,
emax = largest exponent before overflow,
rmax = overflow threshold.