# HPL_dlamch man page

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).