### ===========================================================================
###
### Periodicity of ORCA fields
###
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## SVN information
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def lbc (ptab, nperio=6, cd_type='T', psgn=1.0) :
    # nperio    : Type of periodicity
    #   1, 4, 6 : Cyclic on i dimension (generaly longitudes)
    #   2       : Obsolete (was symmetric condition at southern boundary ?)
    #   3, 4    : North fold T-point pivot (legacy ORCA2)
    #   5, 6    : North fold F-point pivot (ORCA1, ORCA025, ORCA2 with new grid for paleo)
    # ptab     : Input array
    #   rank 2 at least : patb[[...., lat, lon]
    # cd_type  : Grid specification : T, U, V or F
    # psgn     : For change of sign for vector components
    #
    # See NEMO documentation for further details
    
    jpi = ptab.shape[-1]
    
    #
    #> East-West boundary conditions
    # --------------------------------

    if nperio in [1, 4, 6] :
        # ... cyclic
        ptab [...,:,  0] = ptab [...,:,-2]
        ptab [...,:, -1] = ptab [...,:, 1]
   
    #
    #> North-South boundary conditions
    # ----------------------------------
    if nperio in [3, 4] :  # North fold T-point pivot     
        if cd_type in [ 'T', 'W' ] : # T-, W-point
            ptab[..., -1, 1:      ] = psgn * ptab[..., -3, -1:0:-1]      
            ptab[..., -1, 0]        = psgn * ptab[..., -3, 2]
            ptab[..., -2, jpi/2:  ] = psgn * ptab[..., -2, jpi/2:0:-1]
                      
        if cd_type == 'U' :
            ptab[..., -1, 0:-1    ] = psgn * ptab[..., -3, -1:0:-1  ]       
            ptab[..., -1,  0]       = psgn * ptab[..., -3,  1]
            ptab[..., -1, -1]       = psgn * ptab[..., -3, -2] 
            ptab[..., -2, jpi/2-1:] = psgn * ptab[..., -2, jpi/2+1:0:-1]
            
        if cd_type == 'V' : 
            ptab[..., -2, 1:      ] = psgn * ptab[..., -3, jpi-1:0:-1]
            ptab[..., -1, 1:      ] = psgn * ptab[..., -4, -1:0:-1]   
            ptab[..., -1, 0]        = psgn * ptab[..., -4, 2]
            
        if cd_type == 'F' :
            ptab[..., -2, 0:-1    ] = psgn * ptab[..., -3, -1:0:-1]
            ptab[..., -1, 0:-1    ] = psgn * ptab[..., -4, -1:0:-1]
            ptab[..., -1,  0]       = psgn * ptab[..., -4,  1]
            ptab[..., -1, -1]       = psgn * ptab[..., -4, -2] 
      
    if nperio in [5, 6] :            #  North fold F-point pivot  
        if cd_type in ['T', 'W']  :
            ptab[..., -1, 0:      ] = psgn * ptab[..., -2, -1::-1]
                
        if cd_type == 'U' :
            ptab[..., -1, 0:-1    ] = psgn * ptab[..., -2, -2::-1]       
            ptab[..., -1, -1]       = psgn * ptab[..., -2, 0]
             
        if cd_type == 'V' :
            ptab[..., -1, 0:      ] = psgn * ptab[..., -3, -1::-1   ]
            ptab[..., -2, jpi/2:  ] = psgn * ptab[..., -2, jpi/2-1::-1]
                             
        if cd_type == 'F' :
            ptab[..., -1, 0:-1    ] = psgn * ptab[..., -3, -2::-1]
            ptab[..., -1, -1]       = psgn * ptab[..., -3, 0]
            ptab[..., -2, jpi/2:-1] = psgn * ptab[..., -2, jpi/2-2::-1]

    return ptab
################################