snrm2
Calculate the L2-norm of a single-precision floating-point vector.
The L2-norm is defined as
Usage
var snrm2 = require( '@stdlib/blas/base/snrm2' );
snrm2( N, x, stride )
Computes the L2-norm of a single-precision floating-point vector x.
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, -2.0, 2.0 ] );
var z = snrm2( x.length, x, 1 );
// returns 3.0
The function has the following parameters:
- N: number of indexed elements.
- x: input
Float32Array. - stride: index increment for
x.
The N and stride parameters determine which elements in the strided array are accessed at runtime. For example, to compute the L2-norm of every other element in x,
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, 2.0, 2.0, -7.0, -2.0, 3.0, 4.0, 2.0 ] );
var z = snrm2( 4, x, 2 );
// returns 5.0
Note that indexing is relative to the first index. To introduce an offset, use typed array views.
var Float32Array = require( '@stdlib/array/float32' );
var x0 = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var z = snrm2( 4, x1, 2 );
// returns 5.0
If N is less than or equal to 0, the function returns 0.
snrm2.ndarray( N, x, stride, offset )
Computes the L2-norm of a single-precision floating-point vector using alternative indexing semantics.
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, -2.0, 2.0 ] );
var z = snrm2.ndarray( x.length, x, 1, 0 );
// returns 3.0
The function has the following additional parameters:
- offset: starting index for
x.
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 calculate the L2-norm for every other value in x starting from the second value
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ] );
var z = snrm2.ndarray( 4, x, 2, 1 );
// returns 5.0
Notes
Examples
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var snrm2 = require( '@stdlib/blas/base/snrm2' );
var opts = {
'dtype': 'float32'
};
var x = discreteUniform( 10, 0, 100, opts );
console.log( x );
var out = snrm2( x.length, x, 1 );
console.log( out );
C APIs
Usage
#include "stdlib/blas/base/snrm2.h"
c_snrm2( N, *X, stride )
Computes the L2-norm of a complex single-precision floating-point vector.
const float x[] = { 1.0f, 2.0f, 2.0f, -7.0f, -2.0f, 3.0f, 4.0f, 2.0f };
float norm = c_snrm2( 4, x, 2 );
// returns 5.0f
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_snrm2( const CBLAS_INT N, const float *X, const CBLAS_INT stride );
c_snrm2_ndarray( N, *X, stride, offset )
Computes the L2-norm of a complex single-precision floating-point vector using alternative indexing semantics.
const float x[] = { 1.0f, 2.0f, 2.0f, -7.0f, -2.0f, 3.0f, 4.0f, 2.0f };
float norm = c_snrm2_ndarray( 4, x, 2, 0 );
// returns 5.0f
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_snrm2_ndarray( const CBLAS_INT N, const float *X, const CBLAS_INT stride, const CBLAS_INT offset );
Examples
#include "stdlib/blas/base/snrm2.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 indexed elements:
const int N = 8;
// Specify a stride:
const int strideX = 1;
// Compute the L2-norm:
float l2 = c_snrm2( N, x, strideX );
// Print the result:
printf( "L2-norm: %f\n", l2 );
// Compute the L2-norm:
l2 = c_snrm2_ndarray( N, x, -strideX, 7 );
// Print the result:
printf( "L2-norm: %f\n", l2 );
}