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: sq_dist.m
    path of file: ./repos/vbmc/gplite/private
    
    the code of the file until where you have to start completion: % sq_dist - a function to compute a matrix of all pairwise squared distances
% between two sets of vectors, stored in the columns of the two matrices, a
% (of size D by n) and b (of size D by m). If only a single argument is given
% or the second matrix is empty, the missing matrix is taken to be identical
% to the first.
%
% Usage: C = 
    
function to compute a matrix of all pairwise squared distances
% between two sets of vectors, stored in the columns of the two matrices, a
% (of size D by n) and b (of size D by m). If only a single argument is given
% or the second matrix is empty, the missing matrix is taken to be identical
% to the first.
%
% Usage: C = sq_dist(a, b)
%    or: C = sq_dist(a)  or equiv.: C = sq_dist(a, [])
%
% Where a is of size Dxn, b is of size Dxm (or empty), C is of size nxm.
%
% Copyright (c) by Carl Edward Rasmussen and Hannes Nickisch, 2010-12-13.

function C = sq_dist(a, b)

if nargin<1  || nargin>3 || nargout>1, error('Wrong number of arguments.'); end