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_smooth.m
    path of file: ./repos/spm
    
    the code of the file until where you have to start completion: function spm_smooth(P,Q,s,dtype)
% 3 dimensional convolution of an image
% FORMAT spm_smooth(P,Q,s,dtype)
% P     - image(s) to be smoot
    
function smooth1(P,Q,s,dtype)
%==========================================================================
function smooth1(P,Q,s,dtype)

if isstruct(P)
    VOX = sqrt(sum(P.mat(1:3,1:3).^2));
else
    VOX = [1 1 1];
end