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Created by: jdha

a case of lost in translation from the matlab to the python. Original matlab syntax:

function [prot] = nemo_rot_rep(pxin,pyin,cd_type,cdtodo,gcos,gsin)

%  nemo_rot_rep rotate nemo vector components
%     [PROT] = nemo_rot_rep(PXIN,PYIN,CD_TYPE,CDTODO,GCOS,GSIN) adapted
%     from rot_rep NEMO v3.3.1 routine. Rotate the Repere: Change vector 
%     componantes between geographic grid <--> stretched coordinates grid.r
%
%     In:
%           pxin, pyin   ! vector componantes
%           cd_type      ! define the nature of pt2d array grid-points
%           cdtodo       ! specify the work to do:
%                         'en->i' east-north to model i componante
%                         'en->j' east-north to model j componante
%                         'ij->e' model i-j componantes to east componante
%                         'ij->n' model i-j componantes to north componante
%           gcos           rotation angle from nemo_grid_angle.m
%           gsin           rotation angle from nemo_grid_angle.m
%
%     Out:
%           prot
%
%     Example: 
%
%     Author: J Harle (jdha@noc.ac.uk) 24-05-11
%
%     See also  nemo_grid_angle

switch (cdtodo)
 case ('en->i')      % 'en->i' est-north to model i componante
  switch (cd_type)
   case ('T') ;   prot = pxin.*gcos + pyin.*gsin ;
   otherwise  ;   error( 'Only T, U, V and F grid points are coded' )
  end
 case ('en->j')      % 'en->j' est-north to model j componante
  switch (cd_type)
   case ('T') ;   prot = pyin.*gcos - pxin.*gsin ;
   otherwise  ;   error( 'Only T, U, V and F grid points are coded' )
  end
 case ('ij->e')      % 'ij->e' model i-j componantes to est componante
  switch (cd_type)
   case ('T') ;   prot = pxin.*gcos - pyin.*gsin ;
   otherwise  ;   error( 'Only T, U, V and F grid points are coded' )
  end
 case ('ij->n')      % 'ij->n' model i-j componantes to est componante
  switch (cd_type)
   case ('T') ;   prot = pyin.*gcos + pxin.*gsin ;
   otherwise  ;   error( 'Only T, U, V and F grid points are coded' )
  end
 otherwise  ;  error( 'rot_rep: Syntax Error in the definition of cdtodo' )
end

The logic in the python (utils/nemo_bdy_lib.py) appears to be incorrect, try replacing:

def rot_rep(pxin, pyin, dummy, cd_todo, gcos, gsin):
    """rotate function"""
    if cd_todo.lower() in ['en to i', 'ij to e']:
        x_var, y_var = pxin, pyin
    elif cd_todo.lower() in ['en to j', 'ij to n']:
        x_var, y_var = pyin, pxin*-1
    else:
        raise SyntaxError('rot_rep cd_todo %s is invalid' %cd_todo)
    return x_var * gcos + y_var * grin

with:

def rot_rep(pxin, pyin, dummy, cd_todo, gcos, gsin):
    """rotate function"""
    if cd_todo.lower() == 'en to i':
        x_var, y_var = pxin, pyin
    elif cd_todo.lower() == 'en to j':
        x_var, y_var = pyin, pxin*-1
    elif cd_todo.lower() == 'ij to e':
        x_var, y_var = pxin, pyin*-1
    elif cd_todo.lower() == 'ij to n':
        x_var, y_var = pyin, pxin
    else:
        raise SyntaxError('rot_rep cd_todo %s is invalid' %cd_todo)
    return x_var * gcos + y_var * gsin

or similar ... need also to have benchmark in place to verify that this is working (e.g. two tests with U[:,:]=1, V[:,:]=0 and vice versa