function y = jdtest(P)
% JDTEST y = jdtest(P) Tests P for unit total and negative elements
% Version of 10/8/93
M = min(min(P));
S = sum(sum(P));
if M < 0
  y = 'Negative entries';
elseif abs(1 - S) > 1e-7
  y = 'Probabilities do not sum to one';
else
  y = 'P is a valid distribution';
end