dasum
Compute the sum of absolute values (L1 norm).
The L1 norm is defined as
Usage
var dasum = require( '@stdlib/blas/base/dasum' );
dasum( N, x, stride )
Computes the sum of absolute values.
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 ] );
var sum = dasum( x.length, x, 1 );
// returns 19.0
The function has the following parameters:
- N: number of indexed elements.
- x: input
Float64Array. - 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 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 ] );
var sum = dasum( 4, x, 2 );
// returns 10.0
Note that indexing is relative to the first index. To introduce an offset, use typed array views.
var Float64Array = require( '@stdlib/array/float64' );
// 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
// Sum every other value...
var sum = dasum( 3, x1, 2 );
// returns 12.0
If N is less than or equal to 0, the function returns 0.
dasum.ndarray( N, x, stride, offset )
Computes the sum of absolute values using alternative indexing semantics.
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 ] );
var sum = dasum.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 Float64Array = require( '@stdlib/array/float64' );
var x = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
var sum = dasum.ndarray( 3, x, 1, x.length-3 );
// returns 15.0
// Using a negative stride to sum from the last element:
sum = dasum.ndarray( 3, x, -1, x.length-1 );
// returns 15.0
Notes
Examples
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var dasum = require( '@stdlib/blas/base/dasum' );
var opts = {
'dtype': 'float64'
};
var x = discreteUniform( 10, -100, 100, opts );
console.log( x );
var out = dasum( x.length, x, 1 );
console.log( out );
C APIs
Usage
#include "stdlib/blas/base/dasum.h"
c_dasum( N, *X, stride )
Computes the sum of absolute values.
const double x[] = { 1.0, 2.0, 3.0, 4.0 };
double v = c_dasum( 4, x, 1 );
// returns 10.0
The function accepts the following arguments:
- N:
[in] CBLAS_INTnumber of indexed elements. - X:
[in] double*input array. - stride:
[in] CBLAS_INTindex increment forX.
double c_dasum( const CBLAS_INT N, const double *X, const CBLAS_INT stride );
c_dasum_ndarray( N, *X, stride, offset )
Computes the sum of absolute values using alternative indexing semantics.
const double x[] = { 1.0, 2.0, 3.0, 4.0 };
double v = c_dasum_ndarray( 4, x, -1, 3 );
// returns 10.0
The function accepts the following arguments:
- N:
[in] CBLAS_INTnumber of indexed elements. - X:
[in] double*input array. - stride:
[in] CBLAS_INTindex increment forX. - offset:
[in] CBLAS_INTstarting index forX.
double c_dasum_ndarray( const CBLAS_INT N, const double *X, const CBLAS_INT stride, const CBLAS_INT offset );
Examples
#include "stdlib/blas/base/dasum.h"
#include <stdio.h>
int main( void ) {
// Create a strided array:
const double x[] = { 1.0, -2.0, 3.0, -4.0, 5.0, -6.0, 7.0, -8.0 };
// Specify the number of elements:
const int N = 8;
// Specify a stride:
const int strideX = 1;
// Compute the sum of absolute values:
double sum = c_dasum( N, x, strideX );
// Print the result:
printf( "sum: %lf\n", sum );
// Compute the sum of absolute values:
sum = c_dasum_ndarray( N, x, -strideX, N-1 );
// Print the result:
printf( "sum: %lf\n", sum );
}