sqdist.m

Matlab工具包补充算发

function m = sqdist(p, q, A)
% SQDIST      Squared Euclidean or Mahalanobis distance.
% SQDIST(p,q)   returns m(i,j) = (p(:,i) - q(:,j))'*(p(:,i) - q(:,j)).
% SQDIST(p,q,A) returns m(i,j) = (p(:,i) - q(:,j))'*A*(p(:,i) - q(:,j)).

%  From Tom Minka's lightspeed toolbox

[d, pn] = size(p);
[d, qn] = size(q);

if nargin == 2
  
  pmag = sum(p .* p, 1);
  qmag = sum(q .* q, 1);
  m = repmat(qmag, pn, 1) + repmat(pmag', 1, qn) - 2*p'*q;
  %m = ones(pn,1)*qmag + pmag'*ones(1,qn) - 2*p'*q;
  
else

  if isempty(A) | isempty(p)
    error('sqdist: empty matrices');
  end
  Ap = A*p;
  Aq = A*q;
  pmag = sum(p .* Ap, 1);
  qmag = sum(q .* Aq, 1);
  m = repmat(qmag, pn, 1) + repmat(pmag', 1, qn) - 2*p'*Aq;
  
end