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    Metadata details:
    filename: interpolator.m
    path of file: ./repos/tracacode/1911-COAWST/script/mfiles/rutgers/grid
    
    the code of the file until where you have to start completion: function F = interpolator(Ginp, field, Xpath, Ypath, ad_F, varargin)

% INTERPOLATOR: Spatially interpolate a ROMS field to horizontal
%               path/trajectory
%
% F = interpolator(Ginp, field, Xpath, Ypath, ad_F, [options])
%
% Given any 2D or 3D ROMS variable FIELD, linearly interpolate to the
% requested path (Xpath, Ypath) in spherical or Cartesian coordinates.
% If input variable is 3D, the horizontally interpolated values are
% returned at all levels of the s-coordinate.
%
% Output includes elemental cell thicknesses and path segment lengths to
% facilitate spatial integration of the interpolated field.
%
% On Input:
%
%    Ginp        ROMS NetCDF file name (string) containing coordinates
%            or, ROMS grid structure (struct array) with depth arrays so
%                3D variables can be processed (see get_roms_grid.m).
%
%    field       ROMS field to interpolate from (2D or 3D array).
%                  Avoid passing field time records. This function cannot
%                  be used for temporal interpolation.
%
%    Xpath       Longitude (degrees_east) or Cartesian (m) coordinates in
%                  the XI-direction (1D or 2D array).
%
%    Ypath       Latitude (degrees_north) or Cartesian (m) coordinates in
%                  the XI-direction (1D or 2D array).
%
%    [ ad_F ]    Adjoint array of the same size of X if 2D array. If
%                  processing 3D variables, it needs an additional
%                  dimension vertical levels. Not used here but added for
%                  compatability with associated adjoint function.
%
% On Output:
%
%    F           Interpolated field (struct array)
%
%                  F.field      variable to process (2D or 3D)
%                  F.Xgrd       variable X-locations (degrees_east or m)
%                  F.Ygrd       variable Y-locations (degrees_north or m)
%                  F.size       variable size
%                  F.Ctype      variable C-grid type
%                  F.method     interpolation method
%                  F.val        interpolated values at (X,Y) or (X,Y,k)
%                  F.Xval       interpolation X-locations (input Xpath)
%                  F.Yval       interpolation Y-locations (input Ypath)
%                  F.Lindex1    linear indices (I  ,J  ) containing (X,Y)
%                  F.Lindex2    linear indices (I+1,J  ) containing (X,Y)
%                  F.Lindex3    linear indices (I+1,J+1) containing (X,Y)

    
function F = interpolator(Ginp, field, Xpath, Ypath, ad_F, varargin)

% INTERPOLATOR: Spatially interpolate a ROMS field to horizontal
%               path/trajectory
%
% F = interpolator(Ginp, field, Xpath, Ypath, ad_F, [options])
%
% Given any 2D or 3D ROMS variable FIELD, linearly interpolate to the
% requested path (Xpath, Ypath) in spherical or Cartesian coordinates.
% If input variable is 3D, the horizontally interpolated values are
% returned at all levels of the s-coordinate.
%
% Output includes elemental cell thicknesses and path segment lengths to
% facilitate spatial integration of the interpolated field.
%
% On Input:
%
%    Ginp        ROMS NetCDF file name (string) containing coordinates
%            or, ROMS grid structure (struct array) with depth arrays so
%                3D variables can be processed (see get_roms_grid.m).
%
%    field       ROMS field to interpolate from (2D or 3D array).
%                  Avoid passing field time records. This function cannot
%                  be used for temporal interpolation.
%
%    Xpath       Longitude (degrees_east) or Cartesian (m) coordinates in
%                  the XI-direction (1D or 2D array).
%
%    Ypath       Latitude (degrees_north) or Cartesian (m) coordinates in
%                  the XI-direction (1D or 2D array).
%
%    [ ad_F ]    Adjoint array of the same size of X if 2D array. If
%                  processing 3D variables, it needs an additional
%                  dimension vertical levels. Not used here but added for
%                  compatability with associated adjoint function.
%
% On Output:
%
%    F           Interpolated field (struct array)
%
%                  F.field      variable to process (2D or 3D)
%                  F.Xgrd       variable X-locations (degrees_east or m)
%                  F.Ygrd       variable Y-locations (degrees_north or m)
%                  F.size       variable size
%                  F.Ctype      variable C-grid type
%                  F.method     interpolation method
%                  F.val        interpolated values at (X,Y) or (X,Y,k)
%                  F.Xval       interpolation X-locations (input Xpath)
%                  F.Yval       interpolation Y-locations (input Ypath)
%                  F.Lindex1    linear indices (I  ,J  ) containing (X,Y)
%                  F.Lindex2    linear indices (I+1,J  ) containing (X,Y)
%                  F.Lindex3    linear indices (I+1,J+1) containing (X,Y)
%                  F.Lindex4    linear indices (I  ,J+1) containing (X,Y)
%                  F.Jindex     lower-left field J-index containing (X,Y)
%                  F.h          bathymetry at requested (X,Y)
%                  F.dis        distance along the path (in km)
%                  F.dislen     path segment lengths for path integral
%                  F.z_w        cell center depths at requested (X,Y,N+1)
%                  F.z_r        cell face depths at requested (X,Y,N)
%                  F.dz         cell thicknesses at requested (X,Y,N)
%
%    dis, z_r, dz and dislen are returned as 2D variables so that the
%    interpolated output can be plotted with pcolor(F.dis,F.z_r,F.val)
%    and integrated with sum(F.val .* F.dislen .* F.dz)
%
% Notice that this function is adjointed, see ad_interpolator.m.  It can
% be used to set-up functionals in various adjoint based algorithms, like
% adjoint sensitivities.
%
% The output linear indices are as follows:
%
%                     Lindex4           Lindex3
%
%                        4________________3
%                        |                |
%                        |                |
%                        |<---p--->       |
%                        |                |
%                        |........o   :   |     field cell elements
%                        |       .    :   |     containing (Xpath,Ypath)
%                        |       .    q   |     as Matlab array
%                        |       .    :   |
%                        |____________:___|
%                        1                2
%
%                     Lindex1           Lindex2

% svn $Id: interpolator.m 938 2019-01-28 06:35:10Z arango $
%=========================================================================%
%  Copyright (c) 2002-2019 The ROMS/TOMS Group                            %
%    Licensed under a MIT/X style license           John L. Wilkin        %
%    See License_ROMS.txt                           Hernan G. Arango      %
%=========================================================================%

% The input variable ad_F is not used here but it is added
% for compatibility with the adjoint version of this function.
% If given, check it is empty so we know the user is not trying to so
% something with it

if nargin > 4
  if ~isempty(ad_F)
    warning('INTERPOLATOR does not use the ad_F input')
    error('Pass an empty [ ] argument if further inputs are used')
  end