function dirichlet ( x, n )

!*****************************************************************************80
!
!! 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:
!
!    12 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.
!
  implicit none

  integer, parameter :: rk8 = kind ( 1.0D+00 )

  real ( kind = rk8 ) dirichlet
  integer n
  real ( kind = rk8 ) x

  if ( sin ( 0.5D+00 * x ) == 0.0D+00 ) then
    dirichlet = 1.0D+00
  else
    dirichlet = sin ( 0.5D+00 * n * x ) / n / sin ( 0.5D+00 * x )
  end if

  return
end