Daniel@0: function m = sqdist(p, q, A)
Daniel@0: % SQDIST      Squared Euclidean or Mahalanobis distance.
Daniel@0: % SQDIST(p,q)   returns m(i,j) = (p(:,i) - q(:,j))'*(p(:,i) - q(:,j)).
Daniel@0: % SQDIST(p,q,A) returns m(i,j) = (p(:,i) - q(:,j))'*A*(p(:,i) - q(:,j)).
Daniel@0: 
Daniel@0: %  From Tom Minka's lightspeed toolbox
Daniel@0: 
Daniel@0: [d, pn] = size(p);
Daniel@0: [d, qn] = size(q);
Daniel@0: 
Daniel@0: if nargin == 2
Daniel@0:   
Daniel@0:   pmag = sum(p .* p, 1);
Daniel@0:   qmag = sum(q .* q, 1);
Daniel@0:   m = repmat(qmag, pn, 1) + repmat(pmag', 1, qn) - 2*p'*q;
Daniel@0:   %m = ones(pn,1)*qmag + pmag'*ones(1,qn) - 2*p'*q;
Daniel@0:   
Daniel@0: else
Daniel@0: 
Daniel@0:   if isempty(A) | isempty(p)
Daniel@0:     error('sqdist: empty matrices');
Daniel@0:   end
Daniel@0:   Ap = A*p;
Daniel@0:   Aq = A*q;
Daniel@0:   pmag = sum(p .* Ap, 1);
Daniel@0:   qmag = sum(q .* Aq, 1);
Daniel@0:   m = repmat(qmag, pn, 1) + repmat(pmag', 1, qn) - 2*p'*Aq;
Daniel@0:   
Daniel@0: end