# Epsilon
> Difference between one and the smallest value greater than one that can be represented as a [double-precision floating-point number][ieee754].
[Epsilon][machine-epsilon] is defined as
where `b` is the radix (base) and `p` is the precision (number of radix bits in the significand). For [double-precision floating-point numbers][ieee754], `b` is `2` and `p` is `53`.
## Usage
```javascript
var FLOAT64_EPSILON = require( '@stdlib/constants/float64/eps' );
```
#### FLOAT64_EPSILON
Difference between one and the smallest value greater than one that can be represented as a [double-precision floating-point number][ieee754].
```javascript
var bool = ( FLOAT64_EPSILON === 2.220446049250313e-16 );
// returns true
```
## Examples
```javascript
var abs = require( '@stdlib/math/base/special/abs' );
var max = require( '@stdlib/math/base/special/max' );
var randu = require( '@stdlib/random/base/randu' );
var FLOAT64_EPSILON = require( '@stdlib/constants/float64/eps' );
var bool;
var a;
var b;
var i;
function isApprox( a, b ) {
var delta;
var tol;
delta = abs( a - b );
tol = FLOAT64_EPSILON * max( abs( a ), abs( b ) );
return ( delta <= tol );
}
for ( i = 0; i < 100; i++ ) {
a = randu() * 10.0;
b = a + (randu()*5.0e-15) - 2.5e-15;
bool = isApprox( a, b );
console.log( '%d %s approximately equal to %d. Delta: %d.', a, ( bool ) ? 'is' : 'is not', b, abs( a - b ) );
}
```
[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985
[machine-epsilon]: https://en.wikipedia.org/wiki/Machine_epsilon
