ant the
       resulting distance to be a metric, it should be
       at least half the diameter of the space (maximum
       possible distance between any two points). If you
       want partial matching you can set it to zero (but
       then the resulting distance is not guaranteed to be a metric).
       Default value is -1 which means 1*max_element_in_C<DD><CODE>F</CODE> - if not null, F is filled with the flows between all bins, except the flow
       to the extra mass bin.
       Note that EMD and EM