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HPL_pdlamch(3)               HPL Library Functions              HPL_pdlamch(3)


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.

HPL 2.1                        October 26, 2012                 HPL_pdlamch(3)

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