! $Id: cos_window.f90 2022-11-02 09:51:28Z ychen $

!****s* fsi/cos_window *
!
! NAME
!   runav  - This subroutine performs COSINE filter
!
! SYNOPSIS
!    call cos_window(x1, x2, dx1, dx2, x, w)
!
! DESCRIPTION
!    This subroutine performs COSINE filter with dx1, dx2 points at each edges
!
! INPUTS
!    REAL(wp),      :: x1
!    REAL(wp),      :: x2
!    REAL(wp),      :: dx1
!    REAL(wp),      :: dx2
!    REAL(wp),      :: x
!
! OUTPUT
!    REAL(wp),      :: w    cosine weighting
!
! AUTHOR
!   Yong Chen, NOAA/NESDIS/STAR, yong.chen@noaa.gov
!
! COPYRIGHT
!   Copyright (c) 2022-2023 Yong Chen <yong.chen@noaa.gov>
!   For further details please refer to the file COPYRIGHT
!   which you should have received as part of this distribution.
!
!****

SUBROUTINE cos_window(x1, x2, dx1, dx2, x, w)

  USE typesizes, ONLY: wp => EightByteReal
  USE ropp_pp_constants, ONLY: Pi

  IMPLICIT NONE

  REAL(wp),                  INTENT(IN)    :: x1
  REAL(wp),                  INTENT(IN)    :: x2
  REAL(wp),                  INTENT(IN)    :: dx1
  REAL(wp),                  INTENT(IN)    :: dx2
  REAL(wp),                  INTENT(IN)    :: x
  REAL(wp),                  INTENT(OUT)   :: w

  IF ( (x >= x1 + dx1) .and. (x <= x2 - dx2) ) w = 1.0_wp
  IF ( (x <= x1 - dx1) .or.  (x >= x2 + dx2) ) w = 0.0_wp
  IF ( (x < x1 + dx1)  .and. (x > x1 - dx1) )  &
      w = (1.0_wp + dsin(Pi * (x - x1) / dx1 / 2.0_wp) ) / 2.0_wp

  IF ( (x > x2 - dx2)  .and. (x < x2 + dx2) )  &
      w = (1.0_wp - dsin(Pi * (x - x2) / dx2 / 2.0_wp) ) / 2.0_wp

END SUBROUTINE cos_window