# dfill
> Fill a double-precision floating-point strided array with a specified scalar constant.
## Usage
```javascript
var dfill = require( '@stdlib/blas/ext/base/dfill' );
```
#### dfill( N, alpha, x, stride )
Fills a double-precision floating-point strided array `x` with a specified scalar constant `alpha`.
```javascript
var Float64Array = require( '@stdlib/array/float64' );
var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
dfill( x.length, 5.0, x, 1 );
// x => [ 5.0, 5.0, 5.0, 5.0, 5.0, 5.0, 5.0, 5.0 ]
```
The function has the following parameters:
- **N**: number of indexed elements.
- **alpha**: scalar constant.
- **x**: input [`Float64Array`][@stdlib/array/float64].
- **stride**: index increment.
The `N` and `stride` parameters determine which elements in `x` are accessed at runtime. For example, to fill every other element
```javascript
var Float64Array = require( '@stdlib/array/float64' );
var floor = require( '@stdlib/math/base/special/floor' );
var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var N = floor( x.length / 2 );
dfill( N, 5.0, x, 2 );
// x => [ 5.0, 1.0, 5.0, -5.0, 5.0, 0.0, 5.0, -3.0 ]
```
Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
```javascript
var Float64Array = require( '@stdlib/array/float64' );
var floor = require( '@stdlib/math/base/special/floor' );
// Initial array...
var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
// Create an offset view...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var N = floor( x0.length/2 );
// Fill every other element...
dfill( N, 5.0, x1, 2 );
// x0 => [ 1.0, 5.0, 3.0, 5.0, 5.0, 5.0 ]
```
#### dfill.ndarray( N, alpha, x, stride, offset )
Fills a double-precision floating-point strided array `x` with a specified scalar constant `alpha` using alternative indexing semantics.
```javascript
var Float64Array = require( '@stdlib/array/float64' );
var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
dfill.ndarray( x.length, 5.0, x, 1, 0 );
// x => [ 5.0, 5.0, 5.0, 5.0, 5.0, 5.0, 5.0, 5.0 ]
```
The function has the following additional parameters:
- **offset**: starting index.
While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, the `offset` parameter supports indexing semantics based on a starting index. For example, to access only the last three elements of `x`
```javascript
var Float64Array = require( '@stdlib/array/float64' );
var x = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
dfill.ndarray( 3, 5.0, x, 1, x.length-3 );
// x => [ 1.0, -2.0, 3.0, 5.0, 5.0, 5.0 ]
```
## Notes
- If `N <= 0`, both functions return `x` unchanged.
## Examples
```javascript
var round = require( '@stdlib/math/base/special/round' );
var randu = require( '@stdlib/random/base/randu' );
var Float64Array = require( '@stdlib/array/float64' );
var dfill = require( '@stdlib/blas/ext/base/dfill' );
var rand;
var sign;
var x;
var i;
x = new Float64Array( 10 );
for ( i = 0; i < x.length; i++ ) {
rand = round( randu()*100.0 );
sign = randu();
if ( sign < 0.5 ) {
sign = -1.0;
} else {
sign = 1.0;
}
x[ i ] = sign * rand;
}
console.log( x );
dfill( x.length, 5.0, x, 1 );
console.log( x );
```
[@stdlib/array/float64]: https://www.npmjs.com/package/@stdlib/array-float64
[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray