Dirichlet Eta Function

Dirichlet eta function.

The Dirichlet eta function is defined by the Dirichlet series

where s is a complex variable equal to σ + ti. The series is convergent for all complex numbers having a real part greater than 0.

Note that the Dirichlet eta function is also known as the alternating zeta function and denoted ζ*(s). The series is an alternating sum corresponding to the Dirichlet series expansion of the Riemann zeta function. Accordingly, the following relation holds:

where ζ(s) is the Riemann zeta function.

Installation

npm install @stdlib/math-base-special-dirichlet-eta

Usage

var eta = require( '@stdlib/math-base-special-dirichlet-eta' );

eta( s )

Evaluates the Dirichlet eta function for a double-precision floating-point number s.

var v = eta( 0.0 ); // Abel sum of 1-1+1-1+...
// returns 0.5

v = eta( -1.0 ); // Abel sum of 1-2+3-4+...
// returns 0.25

v = eta( 1.0 ); // alternating harmonic series => ln(2)
// returns 0.6931471805599453

v = eta( 3.14 );
// returns ~0.9096

v = eta( NaN );
// returns NaN

Examples

var uniform = require( '@stdlib/random-array-uniform' );
var logEachMap = require( '@stdlib/console-log-each-map' );
var eta = require( '@stdlib/math-base-special-dirichlet-eta' );

var opts = {
    'dtype': 'float64'
};
var s = uniform( 200, -50.0, 50.0, opts );

logEachMap( 's: %0.4f, η(s): %0.4f', s, eta );

C APIs

Usage

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

stdlib_base_eta( s )

Evaluates the Dirichlet eta function for a double-precision floating-point number s.

double y = stdlib_base_eta( 0.0 );
// returns 0.5

The function accepts the following arguments:

• s: [in] double input value.

double stdlib_base_eta( const double s );

Examples

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

int main( void ) {
    const double x[] = { 45.0, 90.0, 0.0, 0.0 / 0.0 };

    double y;
    int i;
    for ( i = 0; i < 4; i++ ) {
        y = stdlib_base_eta( x[ i ] );
        printf( "η(%lf) = %lf\n", x[ i ], y );
    }
}

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

License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.