make_mask Subroutine

   subroutine make_mask(x0, y0, a, b, shap, msk, long, larg)
   !================================================================================================
   !! Mask a region within a given shape (for the moment an ellipsis)
   !------------------------------------------------------------------------------------------------
   implicit none
   integer  (kind=I4), intent(in   )                              :: long  !! *2D array length*
   integer  (kind=I4), intent(in   )                              :: larg  !! *2D array height*
   integer  (kind=I4), intent(in   )                              :: x0    !! *mask shape center 1st coordinate*
   integer  (kind=I4), intent(in   )                              :: y0    !! *mask shape center 2nd coordinate*
   integer  (kind=I4), intent(in   )                              :: a     !! *ellipsis semi-length*
   integer  (kind=I4), intent(in   )                              :: b     !! *ellipsis semi-height*
   character(len = 8), intent(in   )                              :: shap  !! *kind of mask shape*
   integer  (kind=I4), intent(inout), dimension(1:long, 1:larg)   :: msk   !! *mask*

      integer(kind=I4) :: i, j

      select case (shap)

         case('ellipsis')
            forall( i = 1:long, j = 1:larg, (real(i - x0, kind = R8) / a)**2 + (real(j - y0, kind = R8) / b)**2 < 1. ) msk(i, j) = 1

         case default
            stop 'make_mask, bad choice'

      endselect

   return
   endsubroutine make_mask