! -*- Mode: f90 -*-
MODULE formula
   USE declare
   USE modeles
CONTAINS
   ELEMENTAL FUNCTION dedans (pa, x1, x2)  !> TRUE if one point is between to others
      IMPLICIT NONE
      LOGICAL :: dedans
      REAL (kind=rl), INTENT (in) :: pa, x1, x2
      dedans = (pa > MIN (x1, x2)) .AND. (pa <= MAX (x1, x2))
      RETURN
   END FUNCTION dedans
   ! ----------------------------------------------------------------------------
   ELEMENTAL FUNCTION dehors (pa1, pa2, x1, x2) !> TRUE if one segment is disconnected from the other
      IMPLICIT NONE
      LOGICAL :: dehors
      REAL (kind=rl), INTENT (in) :: pa1, pa2, x1, x2
      dehors = (MAX (pa1, pa2) < MIN (x1, x2)) .OR. (MIN (pa1, pa2) > MAX (x1, x2))
      RETURN
   END FUNCTION dehors
   ! ----------------------------------------------------------------------------
   ELEMENTAL FUNCTION clo_lon (zlon, zlon0) !> Find closest longitude
      IMPLICIT NONE
      REAL (kind=rl) :: clo_lon
      REAL (kind=rl), INTENT (in) :: zlon, zlon0
      REAL (kind=rl) :: zz, zp, zm, z0
      INTEGER (kind=il) :: jn
      z0 = zlon
      DO jn = 1_il, 2_il
         zz = ABS ((z0          ) - zlon0)
         zp = ABS ((z0 + 360.0_rl) - zlon0)
         zm = ABS ((z0 - 360.0_rl) - zlon0)
         IF (     zp < MIN (zm, zz)) THEN 
            z0 = z0 + 360.0_rl
         ELSE IF (zm < MIN (zp, zz)) THEN 
            z0 = z0 - 360.0_rl
         END IF
      END DO
      clo_lon = z0
   END FUNCTION clo_lon
   ! ----------------------------------------------------------------------------
   ELEMENTAL FUNCTION lon_180 (zlon) !> Set lon in [0-360]
      REAL (kind=rl) :: lon_180
      REAL (kind=rl), INTENT (in) :: zlon
      REAL (kind=rl) :: z0
      z0 = zlon
      IF ( z0 <   0.0_rl) z0 = z0 + 360.0_rl
      IF ( z0 > 360.0_rl) z0 = z0 - 360.0_rl
      lon_180 = z0
   END FUNCTION lon_180

  ! ----------------------------------------------------------------------------
!$$$  FUNCTION tri_surf (plon, plat) !> Surface of triangle on the sphere
!$$$    USE declare
!$$$    IMPLICIT NONE
!$$$    REAL (kind=rl) :: tri_surf
!$$$    REAL (kind=rl), DIMENSION (3), INTENT (in) :: plon, plat
!$$$    tri_surf = 0.0_rl
!$$$  END FUNCTION tri_surf
!$$$  !! 
END MODULE formula