# Name

**HPL_pdlamch**determines machine-specific arithmetic constants.

# Synopsis

`#include "hpl.h"`

`double`

`HPL_pdlamch(`

`MPI_Comm`

`COMM`

,
`const HPL_T_MACH`

`CMACH`

`);`

# Description

**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).

# Arguments

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 where 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.