Returns True if the variable D passed is a valid distance matrix. Distance matrices must be 2dimensional numpy arrays containing doubles. They must have a zerodiagonal, and they must be symmetric.
Parameters :  D : ndarray
tol : double throw : bool
name : string
warning : bool


Returns :  Returns ``True`` if the variable ``D`` passed is a valid : distance matrix. Small numerical differences in ``D`` and : ``D.T`` and nonzeroness of the diagonal are ignored if they are : within the tolerance specified by ``tol``. : 