You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: ft_warp_apply.m
    path of file: ./repos/spm12/external/fieldtrip/utilities
    
    the code of the file until where you have to start completion: function [warped] = ft_warp_apply(M, input, method, tol)

% FT_WARP_APPLY performs a 3D linear or nonlinear transformation on the input
% coordinates, similar to those in AIR. You can find technical documentation
% on warping in general at http://air.bmap.ucla.edu/AIR5
%
% Use as
%   [warped] = ft_warp_apply(M, input, method, tol)
% where
%   M        vector or matrix with warping parameters
%   input    Nx3 matrix with coordinates
%   warped   Nx3 matrix with coordinates
%   metho
    
function that returns a homogeneous transformation matrix
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
elseif exist(method, 'file') && ~isa(M, 'struct')
  % get the homogenous transformation matrix
  H = feval(method, M);
  warped = ft_warp_apply(H, input, 'homogeneous');

elseif strcmp(method, 'sn2individual') && isa(M, 'struct')
  % use SPM structure with parameters for an inverse warp
  % from normalized space to individual, can be non-linear
  warped = sn2individual(M, input);

elseif strcmp(method, 'individual2sn') && isa(M, 'struct')
  % use SPM structure with parameters for a warp from
  % individual space to normalized space, can be non-linear
  %error('individual2sn is not yet implemented');
  warped = individual2sn(M, input);
else
  ft_error('unrecognized transformation method');
end