anchor.diff:    real(dp), intent(in)     :: x,y
     real(dp)                 :: psi
   
  -  psi = half*(x*x+y*y)
  +  psi = half*(x*x+y*y+x*y)
   
     end function psifunc
   
  
positive.code: dy = 0.01
  ofile = 'streamline.nc'
  
  call lineargs_ini(na)
  
  call argflg('-A',agrid)
  call argflg('-C',cgrid)
  call argdbl('-dx',fdx,dx)
  
negative.code: 
  implicit none
  
  character(len=*), parameter             :: version = 'v0.1'
  character(len=*), parameter             :: author  = 'Quim Ballabrera'
  
  ! ... I/O flags and options
  ! ...
  logical                                 :: out   = .false.
  logical                                 :: agrid = .false.
  logical                                 :: cgrid = .false.
  logical                                 :: fdx   = .false.
  logical                                 :: fdy   = .false.
  logical                                 :: hlp   = .false.
  
  ! ...
  integer na,nx,ny,i,j,err,fid,idi,idj,idx,idy,idp,idu,idv
  integer idxp,idyp,idxu,idyu,idxv,idyv
  real(dp)  dx,dy
  real(dp), dimension(:), allocatable     :: x,y
  real(dp), dimension(:), allocatable     :: xu,yu
  real(dp), dimension(:), allocatable     :: xv,yv
  real(dp), dimension(:,:), allocatable   :: psi,u,v
  character(len=180)                      :: ofile
  
  ! ... The help
  ! ...
  call help_version(version)
  call help_progname('STREAMLINE')
  call help_author(author)
  call help_summary('Program to calculate the velocity field from an &
   &analytical stream function. The velocity field can be writen in an &
   &Arakawa A or Arakawa C grid. To change the analytic function, the &
   &user needs to modify subroutine UDF before compiling the program.')
  call help_option('-out    FILENAME','Output filename','streamline.nc')
  call help_option('-A              ','Output in Arakawa A grid','A')
  call help_option('-C              ','Output in Arakawa C grid','')
  call help_option('-dx             DX','Zonal grid interval','0.01')
  call help_option('-dy             DY','Meridional grid interval','0.01')
  call help_option ('--options  filename','To read the commandline options &
    &from a file.','')
  call help_option ('--help','To show this help','')
  call help_example ('> streamline -C -o c_grid.nc')
  
  
  ! ... Default values:
  ! ...
  