# roundb
> Round a numeric value to the nearest multiple of b^n on a linear scale.
## Usage
```javascript
var roundb = require( '@stdlib/math/base/special/roundb' );
```
#### roundb( x, n, b )
Rounds a `numeric` value to the nearest multiple of `b^n` on a linear scale.
```javascript
// Round a value to 2 decimal places:
var v = roundb( 3.141592653589793, -2, 10 );
// returns 3.14
// If n = 0 or b = 1, `roundb` behaves like `round`:
v = roundb( 3.141592653589793, 0, 2 );
// returns 3.0
// Round a value to the nearest multiple of two:
v = roundb( 5.0, 1, 2 );
// returns 6.0
```
## Notes
- Due to rounding error in [floating-point numbers][ieee754], rounding may **not** be exact. For example,
```javascript
var x = 0.2 + 0.1;
// returns 0.30000000000000004
// Should round to 0.3...
var v = roundb( x, -16, 10 );
// returns 0.3000000000000001
```
## Examples
```javascript
var randu = require( '@stdlib/random/base/randu' );
var round = require( '@stdlib/math/base/special/round' );
var pow = require( '@stdlib/math/base/special/pow' );
var roundb = require( '@stdlib/math/base/special/roundb' );
var x;
var n;
var b;
var v;
var i;
for ( i = 0; i < 100; i++ ) {
x = (randu()*100.0) - 50.0;
n = round( (randu()*10.0) - 5.0 );
b = round( randu()*10.0 );
v = roundb( x, n, b );
console.log( 'x: %d. %d^%d: %d. Rounded: %d.', x, b, n, pow( b, n ), v );
}
```
[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985