kernelCos

Compute the cosine of a double-precision floating-point number on [-π/4, π/4].

Installation

npm install @stdlib/math-base-special-kernel-cos

Usage

var kernelCos = require( '@stdlib/math-base-special-kernel-cos' );

kernelCos( x, y )

Computes the cosine of a double-precision floating-point number on [-π/4, π/4].

var v = kernelCos( 0.0, 0.0 );
// returns ~1.0

v = kernelCos( 3.141592653589793/6.0, 0.0 );
// returns ~0.866

v = kernelCos( 0.785, -1.144e-17 );
// returns ~0.707

v = kernelCos( NaN, 0.0 );
// returns NaN

Notes

• For increased accuracy, the number for which the cosine should be evaluated can be supplied as a double-double number (i.e., a non-evaluated sum of two double-precision floating-point numbers x and y).

• As components of a double-double number, the two double-precision floating-point numbers x and y must satisfy

  where ulp stands for units in the last place.

Examples

var linspace = require( '@stdlib/array-base-linspace' );
var PI = require( '@stdlib/constants-float64-pi' );
var kernelCos = require( '@stdlib/math-base-special-kernel-cos' );

var x = linspace( -PI/4.0, PI/4.0, 100 );

var i;
for ( i = 0; i < x.length; i++ ) {
    console.log( 'kernelCos(%d) = %d', x[ i ], kernelCos( x[ i ], 0.0 ) );
}

C APIs

Usage

#include "stdlib/math/base/special/kernel_cos.h"

stdlib_base_kernel_cos( x, y )

Computes the cosine of a double-precision floating-point number on [-π/4, π/4].

var v = stdlib_base_kernel_cos( 0.0, 0.0 );
// returns ~0.0

v = stdlib_base_kernel_cos( 3.141592653589793/6.0, 0.0 );
// returns ~0.866

The function accepts the following arguments:

• x: [in] double input value (in radians, assumed to be bounded by ~pi/4 in magnitude).
• y: [in] double tail of x.

double stdlib_base_kernel_cos( const double x, const double y );

Notes

• For increased accuracy, the number for which the cosine should be evaluated can be supplied as a double-double number (i.e., a non-evaluated sum of two double-precision floating-point numbers x and y).

Examples

#include "stdlib/math/base/special/kernel_cos.h"
#include <stdio.h>

int main( void ) {
    const double x[] = { -0.7853981633974483, -0.6108652381980153, -0.4363323129985824, -0.26179938779914946, -0.08726646259971649, 0.08726646259971649, 0.26179938779914935, 0.43633231299858233, 0.6108652381980153, 0.7853981633974483 };
    
    double out;
    int i;
    for ( i = 0; i < 10; i++ ) {
        out = stdlib_base_kernel_cos( x[ i ], 0.0 );
        printf ( "x[ i ]: %lf, y: %lf, out: %lf\n", x[ i ], 0.0, out );
    }
}

See Also

• @stdlib/math-base/special/cos: compute the cosine of a number.
• @stdlib/math-base/special/kernel-sin: compute the sine of a double-precision floating-point number on [-π/4, π/4].
• @stdlib/math-base/special/kernel-tan: compute the tangent of a double-precision floating-point number on [-π/4, π/4].

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.

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Copyright

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