sdot
Calculate the dot product of two single-precision floating-point vectors.
The dot product (or scalar product) is defined as
Usage
var sdot = require( '@stdlib/blas/base/sdot' );
sdot( N, x, strideX, y, strideY )
Calculates the dot product of vectors x and y.
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 4.0, 2.0, -3.0, 5.0, -1.0 ] );
var y = new Float32Array( [ 2.0, 6.0, -1.0, -4.0, 8.0 ] );
var z = sdot( x.length, x, 1, y, 1 );
// returns -5.0
The function has the following parameters:
- N: number of indexed elements.
- x: input
Float32Array. - strideX: index increment for
x. - y: input
Float32Array. - strideY: index increment for
y.
The N and stride parameters determine which elements in the strided arrays are accessed at runtime. For example, to calculate the dot product of every other value in x and the first N elements of y in reverse order,
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Float32Array( [ 1.0, 1.0, 1.0, 1.0, 1.0, 1.0 ] );
var z = sdot( 3, x, 2, y, -1 );
// returns 9.0
Note that indexing is relative to the first index. To introduce an offset, use typed array views.
var Float32Array = require( '@stdlib/array/float32' );
// Initial arrays...
var x0 = new Float32Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y0 = new Float32Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );
// Create offset views...
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var y1 = new Float32Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element
var z = sdot( 3, x1, -2, y1, 1 );
// returns 128.0
sdot.ndarray( N, x, strideX, offsetX, y, strideY, offsetY )
Calculates the dot product of x and y using alternative indexing semantics.
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 4.0, 2.0, -3.0, 5.0, -1.0 ] );
var y = new Float32Array( [ 2.0, 6.0, -1.0, -4.0, 8.0 ] );
var z = sdot.ndarray( x.length, x, 1, 0, y, 1, 0 );
// returns -5.0
The function has the following additional parameters:
- offsetX: starting index for
x. - offsetY: starting index for
y.
While typed array views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example, to calculate the dot product of every other value in x starting from the second value with the last 3 elements in y in reverse order
var Float32Array = require( '@stdlib/array/float32' );
var x = new Float32Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Float32Array( [ 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 ] );
var z = sdot.ndarray( 3, x, 2, 1, y, -1, y.length-1 );
// returns 128.0
Notes
Examples
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var sdot = require( '@stdlib/blas/base/sdot' );
var opts = {
'dtype': 'float32'
};
var x = discreteUniform( 10, 0, 100, opts );
console.log( x );
var y = discreteUniform( x.length, 0, 10, opts );
console.log( y );
var out = sdot( x.length, x, 1, y, -1 );
console.log( out );
C APIs
Usage
#include "stdlib/blas/base/sdot.h"
c_sdot( N, *X, strideX, *Y, strideY )
Computes the dot product of two single-precision floating-point vectors.
const float x[] = { 4.0f, 2.0f, -3.0f, 5.0f, -1.0f };
const float y[] = { 2.0f, 6.0f, -1.0f, -4.0f, 8.0f };
float d = c_sdot( 5, x, 1, y, 1 );
// returns -5.0f
The function accepts the following arguments:
- N:
[in] CBLAS_INTnumber of indexed elements. - X:
[in] float*first input array. - strideX:
[in] CBLAS_INTindex increment forX. - Y:
[in] float*second input array. - strideY:
[in] CBLAS_INTindex increment forY.
float c_sdot( const CBLAS_INT N, const float *X, const CBLAS_INT strideX, const float *Y, const CBLAS_INT strideY );
c_sdot_ndarray( N, *X, strideX, offsetX, *Y, strideY, offsetY )
Computes the dot product of two single-precision floating-point vectors using alternative indexing semantics.
const float x[] = { 4.0f, 2.0f, -3.0f, 5.0f, -1.0f };
const float y[] = { 2.0f, 6.0f, -1.0f, -4.0f, 8.0f };
float d = c_sdot_ndarray( 3, x, 1, 2, y, 1, 2 );
// returns -25.0f
The function accepts the following arguments:
- N:
[in] CBLAS_INTnumber of indexed elements. - X:
[in] float*first input array. - strideX:
[in] CBLAS_INTindex increment forX. - offsetX:
[in] CBLAS_INTstarting index forX. - Y:
[in] float*second input array. - strideY:
[in] CBLAS_INTindex increment forY. - offsetY:
[in] CBLAS_INTstarting index forY.
float c_sdot_ndarray( const CBLAS_INT N, const float *X, const CBLAS_INT strideX, const CBLAS_INT offsetX, const float *Y, const CBLAS_INT strideY, const CBLAS_INT offsetY );
Examples
#include "stdlib/blas/base/sdot.h"
#include <stdio.h>
int main( void ) {
// Create strided arrays:
const float x[] = { 1.0f, -2.0f, 3.0f, -4.0f, 5.0f, -6.0f, 7.0f, -8.0f };
const float y[] = { 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 strides:
const int strideX = 1;
const int strideY = -1;
// Compute the dot product:
float d = c_sdot( N, x, strideX, y, strideY );
// Print the result:
printf( "dot product: %f\n", d );
// Compute the dot product:
d = c_sdot_ndarray( N, x, strideX, 0, y, strideY, 7 );
// Print the result:
printf( "dot product: %f\n", d );
}