# include <math.h>
# include <stdlib.h>

# include "dirichlet.h"

/******************************************************************************/

double dirichlet ( double x, int n )

/******************************************************************************/
/*
  Purpose:

    dirichlet() evaluates the Dirichlet kernel function.

  Discussion:

    The Dirichlet kernel function is also called the periodic sinc function.

  Licensing:

    This code is distributed under the MIT license.

  Modified:

    13 July 2025

  Author:

    John Burkardt

  Input:

    real x: the argument of the function.

    integer n: the degree of the function.

  Output:

    real dirichlet: the value of the function.
*/
{
  double value;

  if ( sin ( 0.5 * x ) == 0.0 )
  {
    value = 1.0;
  }
  else
  {
    value = sin ( 0.5 * n * x ) / n / sin ( 0.5 * x );
  }

  return value;
}