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: spm_orth.m
    path of file: ./repos/ExploreASL/External/SPMmodified
    
    the code of the file until where you have to start completion: function X = spm_orth(X,OPT)
% Recursive Gram-Schmidt orthogonalisation of basis functions
% FORMAT X = spm_orth(X,OPT)

    
function X = spm_orth(X,OPT)
% Recursive Gram-Schmidt orthogonalisation of basis functions
% FORMAT X = spm_orth(X,OPT)
%
% X   - matrix
% OPT - 'norm' for Euclidean normalisation
%     - 'pad'  for zero padding of null space [default]
%
% Serial orthogonalisation starting with the first column
%
% Reference:
% Golub, Gene H. & Van Loan, Charles F. (1996), Matrix Computations (3rd
% ed.), Johns Hopkins, ISBN 978-0-8018-5414-9.
%__________________________________________________________________________
% Copyright (C) 2002-2012 Wellcome Trust Centre for Neuroimaging
 
% Karl Friston
% $Id: spm_orth.m 5821 2013-12-31 14:26:41Z karl $
 

%-Default
%--------------------------------------------------------------------------
try
    OPT;
catch
    OPT = 'pad';
end