# NAG C Library Function Document

## 1Purpose

nag_machine_precision (X02AJC) returns $\epsilon$, the value machine precision.

## 2Specification

 #include #include
 double nag_machine_precision

## 3Description

nag_machine_precision (X02AJC) is a constant defined in the C Header file.
nag_machine_precision (X02AJC) returns machine precision, computed as $\epsilon =\frac{1}{2}×{b}^{1-p}$, where $b$ is the arithmetic base (see nag_real_base (X02BHC)) and $p$ is the number of significant base-$b$ digits (see nag_real_base_digits (X02BJC)).
It is important to note that the definition of $\epsilon$ here differs from that in ISO Fortran 95 (1997).

## 4References

ISO Fortran 95 (1997) ISO Fortran 95 programming language (ISO/IEC 1539–1:1997)

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## 8Parallelism and Performance

nag_machine_precision (X02AJC) is not threaded in any implementation.