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HPL_dlamch(3)                HPL Library Functions               HPL_dlamch(3)


NAME

       HPL_dlamch - determines machine-specific arithmetic constants.


SYNOPSIS

       #include "hpl.h"

       double HPL_dlamch( const HPL_T_MACH CMACH );


DESCRIPTION

       HPL_dlamch 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

       CMACH   (local input)           const HPL_T_MACH
               Specifies the value to be returned by HPL_dlamch
                  = HPL_MACH_EPS,   HPL_dlamch := eps (default)
                  = HPL_MACH_SFMIN, HPL_dlamch := sfmin
                  = HPL_MACH_BASE,  HPL_dlamch := base
                  = HPL_MACH_PREC,  HPL_dlamch := eps*base
                  = HPL_MACH_MLEN,  HPL_dlamch := t
                  = HPL_MACH_RND,   HPL_dlamch := rnd
                  = HPL_MACH_EMIN,  HPL_dlamch := emin
                  = HPL_MACH_RMIN,  HPL_dlamch := rmin
                  = HPL_MACH_EMAX,  HPL_dlamch := emax
                  = HPL_MACH_RMAX,  HPL_dlamch := 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.


EXAMPLE

       #include "hpl.h"

       int main(int argc, char *argv[])
       {
          double eps;
          eps = HPL_dlamch( HPL_MACH_EPS );
          printf("eps=%18.8e\n", eps);
          exit(0); return(0);
       }


REFERENCES

       This function has been manually translated from the Fortran 77 LAPACK
       auxiliary function dlamch.f  (version 2.0 -- 1992), that  was  itself
       based on the function ENVRON  by Malcolm and incorporated suggestions
       by Gentleman and Marovich. See

       Malcolm M. A.,  Algorithms  to  reveal  properties  of floating-point
       arithmetic.,  Comms. of the ACM, 15, 949-951 (1972).

       Gentleman W. M. and Marovich S. B.,  More  on algorithms  that reveal
       properties of  floating point arithmetic units.,  Comms. of  the ACM,
       17, 276-277 (1974).

HPL 2.1                        October 26, 2012                  HPL_dlamch(3)

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