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: transform2grid.m
    path of file: ./repos/fieldtrip/private
    
    the code of the file until where you have to start completion: function [volume] = transform2grid(volume)

% TRANSFORM2GRID ensures that the volume contains the definition of the

    
function [volume] = transform2grid(volume)

% TRANSFORM2GRID ensures that the volume contains the definition of the
% cardian axes, i.e. xgrid/ygrid/zgrid. If the voluyme contains a
% homogenous coordinate transformation axis that is unequal to eye(4), it
% will try to construct the cardinal axis from that transformation matrix.
%
% See also GRID2TRANSFORM

if ~isfield(volume, 'xgrid'),     volume.xgrid=1:volume.dim(1); end