demo_atan2.f90

      program demo_atan2
      real :: z
      complex :: c
       !
       ! basic usage
        ! ATAN2 (1.5574077, 1.0) has the value 1.0 (approximately).
        z=atan2(1.5574077, 1.0)
        write(*,*) 'radians=',z,'degrees=',r2d(z)
       !
       ! elemental arrays
        write(*,*)'elemental',atan2( [10.0, 20.0], [30.0,40.0] )
       !
       ! elemental arrays and scalars
        write(*,*)'elemental',atan2( [10.0, 20.0], 50.0 )
       !
       ! break complex values into real and imaginary components
       ! (note TAN2() can take a complex type value )
        c=(0.0,1.0)
        write(*,*)'complex',c,atan2( x=c%re, y=c%im )
       !
       ! extended sample converting cartesian coordinates to polar
        COMPLEX_VALS: block
        real                :: ang, radius
        complex,allocatable :: vals(:)
        integer             :: i
       !
        vals=[ &
          ( 1.0, 0.0 ), & ! 0
          ( 1.0, 1.0 ), & ! 45
          ( 0.0, 1.0 ), & ! 90
          (-1.0, 1.0 ), & ! 135
          (-1.0, 0.0 ), & ! 180
          (-1.0,-1.0 ), & ! 225
          ( 0.0,-1.0 )]   ! 270
        do i=1,size(vals)
           call cartesian_to_polar(vals(i)%re, vals(i)%im, radius,ang)
           write(*,101)vals(i),ang,r2d(ang),radius
        enddo
        101 format(             &
        & 'X= ',f5.2,           &
        & ' Y= ',f5.2,          &
        & ' ANGLE= ',g0,        &
        & T38,'DEGREES= ',g0.4, &
        & T54,'DISTANCE=',g0)
       endblock COMPLEX_VALS
      !
      contains
      !
      elemental real function r2d(radians)
      ! input radians to convert to degrees
      doubleprecision,parameter :: DEGREE=0.017453292519943d0 ! radians
      real,intent(in)           :: radians
         r2d=radians / DEGREE ! do the conversion
      end function r2d
      !
      subroutine cartesian_to_polar(x,y,radius,inclination)
      ! return angle in radians in range 0 to 2*PI
      implicit none
      real,intent(in)  :: x,y
      real,intent(out) :: radius,inclination
         radius=sqrt(x**2+y**2)
         if(radius.eq.0)then
            inclination=0.0
         else
            inclination=atan2(y,x)
            if(inclination < 0.0)inclination=inclination+2*atan2(0.0d0,-1.0d0)
         endif
      end subroutine cartesian_to_polar
      !
      end program demo_atan2