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sscal

Multiply a single-precision floating-point vector x by a constant alpha.

Installation

npm install @stdlib/blas-base-sscal

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

var sscal = require( '@stdlib/blas-base-sscal' );

sscal( N, alpha, x, stride )

Multiplies a single-precision floating-point vector x by a constant alpha.

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 ] );

sscal( x.length, 5.0, x, 1 );
// x => <Float32Array>[ -10.0, 5.0, 15.0, -25.0, 20.0, 0.0, -5.0, -15.0 ]

The function has the following parameters:

• N: number of indexed elements.
• alpha: scalar constant.
• x: input Float32Array.
• stride: index increment.

The N and stride parameters determine which elements in x are accessed at runtime. For example, to multiply every other value by a constant

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 ] );

sscal( 4, 5.0, x, 2 );
// x => <Float32Array>[ -10.0, 1.0, 15.0, -5.0, 20.0, 0.0, -5.0, -3.0 ]

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

// Scale every other value:
sscal( 3, 5.0, x1, 2 );
// x0 => <Float32Array>[ 1.0, -10.0, 3.0, -20.0, 5.0, -30.0 ]

If either N or stride is less than or equal to 0, the function returns x unchanged.

sscal.ndarray( N, alpha, x, stride, offset )

Multiplies a single-precision floating-point vector x by a constant alpha 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 ] );

sscal.ndarray( x.length, 5.0, x, 1, 0 );
// x => <Float32Array>[ -10.0, 5.0, 15.0, -25.0, 20.0, 0.0, -5.0, -15.0 ]

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 multiply the last three elements of x by a constant

var Float32Array = require( '@stdlib/array-float32' );

var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );

sscal.ndarray( 3, 5.0, x, 1, x.length-3 );
// x => <Float32Array>[ 1.0, -2.0, 3.0, -20.0, 25.0, -30.0 ]

Notes

• If N <= 0, both functions return x unchanged.
• sscal() corresponds to the BLAS level 1 function sscal.

Examples

var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var sscal = require( '@stdlib/blas-base-sscal' );

var opts = {
    'dtype': 'float32'
};
var x = discreteUniform( 10, -100, 100, opts );
console.log( x );

sscal( x.length, 5.0, x, 1 );
console.log( x );

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C APIs

Usage

#include "stdlib/blas/base/sscal.h"

c_sscal( N, alpha, *X, stride )

Multiplies each element of a single-precision floating-point vector by a constant.

float x[] = { 1.0f, 2.0f, 3.0f, 4.0f };

c_sscal( 4, 5.0f, x, 1 );

The function accepts the following arguments:

• N: [in] CBLAS_INT number of indexed elements.
• alpha: [in] float scalar constant.
• X: [inout] float* input array.
• stride: [in] CBLAS_INT index increment for X.

void c_sscal( const CBLAS_INT N, const float alpha, float *X, const CBLAS_INT stride );

c_sscal_ndarray( N, alpha, *X, stride, offset )

Multiplies each element of a single-precision floating-point vector by a constant using alternative indexing semantics.

float x[] = { 1.0f, 2.0f, 3.0f, 4.0f };

c_sscal_ndarray( 4, 5.0f, x, 1, 0 );

The function accepts the following arguments:

• N: [in] CBLAS_INT number of indexed elements.
• alpha: [in] float scalar constant.
• X: [inout] float* input array.
• stride: [in] CBLAS_INT index increment for X.
• offset: [in] CBLAS_INT starting index for X.

void c_sscal_ndarray( const CBLAS_INT N, const float alpha, float *X, const CBLAS_INT stride, const CBLAS_INT offset );

Examples

#include "stdlib/blas/base/sscal.h"
#include <stdio.h>

int main( void ) {
    // Create a strided array:
    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;

    // Scale the vector:
    c_sscal( N, 5.0f, x, stride );

    // Print the result:
    for ( int i = 0; i < 8; i++ ) {
        printf( "x[ %i ] = %f\n", i, x[ i ] );
    }

    // Scale the vector using alternative indexing semantics:
    c_sscal_ndarray( N, 5.0f, x, -stride, N-1 );

    // Print the result:
    for ( int i = 0; i < 8; i++ ) {
        printf( "x[ %i ] = %f\n", i, x[ i ] );
    }
}

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See Also

• @stdlib/blas-base/daxpy: multiply a vector x by a constant and add the result to y.
• @stdlib/blas-base/dscal: multiply a double-precision floating-point vector by a constant.
• @stdlib/blas-base/gscal: multiply a vector by a constant.
• @stdlib/blas-base/saxpy: multiply a vector x by a constant and add the result to y.

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Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.