sasum
Compute the sum of absolute values (L1 norm).
The L1 norm is defined as
Usage
var sasum = require( '@stdlib/blas/base/sasum' );
sasum( N, x, stride )
Computes the sum of absolute values.
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var sum = sasum( x.length, x, 1 );
// returns 19.0
The function has the following parameters:
- N: number of elements to sum.
- x: input
Float32Array
. - stride: index increment.
The N
and stride
parameters determine which elements in x
are used to compute the sum. For example, to sum every other value,
var Float32Array = require( '@stdlib/array/float32' );
var floor = require( '@stdlib/math/base/special/floor' );
var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var N = floor( x.length / 2 );
var stride = 2;
var sum = sasum( N, x, stride );
// returns 10.0
Note that indexing is relative to the first index. To introduce an offset, use typed array
views.
var Float32Array = require( '@stdlib/array/float32' );
var floor = require( '@stdlib/math/base/special/floor' );
// Initial array...
var x0 = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
// Create an offset view...
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var N = floor( x0.length / 2 );
// Sum every other value...
var sum = sasum( N, x1, 2 );
// returns 12.0
If either N
or stride
is less than or equal to 0
, the function returns 0
.
sasum.ndarray( N, x, stride, offset )
Computes the sum of absolute values using alternative indexing semantics.
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var sum = sasum.ndarray( x.length, x, 1, 0 );
// returns 19.0
The function has the following additional parameters:
- offset: starting index.
While 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 sum the last three elements,
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
var sum = sasum.ndarray( 3, x, 1, x.length-3 );
// returns 15.0
// Using a negative stride to sum from the last element:
sum = sasum.ndarray( 3, x, -1, x.length-1 );
// returns 15.0
Notes
Examples
var round = require( '@stdlib/math/base/special/round' );
var randu = require( '@stdlib/random/base/randu' );
var Float32Array = require( '@stdlib/array/float32' );
var sasum = require( '@stdlib/blas/base/sasum' );
var rand;
var sign;
var x;
var i;
x = new Float32Array( 100 );
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( sasum( x.length, x, 1 ) );