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 indexed elements.
- 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 x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var sum = sasum( 4, x, 2 );
// 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' );
// 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
// Sum every other value:
var sum = sasum( 3, x1, 2 );
// returns 12.0
If either N 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 discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var sasum = require( '@stdlib/blas/base/sasum' );
var opts = {
'dtype': 'float32'
};
var x = discreteUniform( 10, -100, 100, opts );
console.log( x );
var out = sasum( x.length, x, 1 );
console.log( out );
C APIs
Usage
#include "stdlib/blas/base/sasum.h"
c_sasum( N, *X, stride )
Computes the sum of absolute values.
const float x[] = { 1.0f, -2.0f, 3.0f, -4.0f, 5.0f, -6.0f, 7.0f, -8.0f };
float sum = c_sasum( 8, x, 1 );
// returns 36.0f
The function accepts the following arguments:
- N:
[in] CBLAS_INTnumber of indexed elements. - X:
[in] float*input array. - stride:
[in] CBLAS_INTindex increment forX.
float c_sasum( const CBLAS_INT N, const float *X, const CBLAS_INT stride );
c_sasum_ndarray( N, *X, stride, offset )
Computes the sum of absolute values using alternative indexing semantics.
const float x[] = { 1.0f, -2.0f, 3.0f, -4.0f, 5.0f, -6.0f, 7.0f, -8.0f };
float sum = c_sasum_ndarray( 8, x, -1, 7 );
// returns 36.0f
The function accepts the following arguments:
- N:
[in] CBLAS_INTnumber of indexed elements. - X:
[in] float*input array. - stride:
[in] CBLAS_INTindex increment forX. - offset:
[in] CBLAS_INTstarting index forX.
float c_sasum_ndarray( const CBLAS_INT N, const float *X, const CBLAS_INT stride, const CBLAS_INT offset );
Examples
#include "stdlib/blas/base/sasum.h"
#include <stdio.h>
int main( void ) {
// Create a strided array:
const float x[] = { 1.0f, -2.0f, 3.0f, -4.0f, 5.0f, -6.0f, 7.0f, -8.0f };
// Specify the number of elements:
const int N = 8;
// Specify a stride:
const int stride = 1;
// Compute the sum of absolute values:
float sum = c_sasum( N, x, stride );
// Print the result:
printf( "sum: %f\n", sum );
// Compute the sum of absolute values:
sum = c_sasum_ndarray( N, x, -stride, N-1 );
// Print the result:
printf( "sum: %f\n", sum );
}