prtDistanceCityBlock   City block distance
  
    DIST = prtDistanceCityBlock(DS1,DS2) calculates the City Block distance
    from all the observations in datasets DS1 to DS2, and ouputs a distance
    matrix of size DS1.nObservations x DS2.nObservations. DS1 and DS2
    should have the same number of features. DS1 and DS2 should be
    prtDataSet objects.
    
    For more information, see:
    
    http://en.wikipedia.org/wiki/Taxicab_geometry
 
  Example:
 
    % Create 2 data sets
    dsx = prtDataSetStandard('Observations', [0 0; 1 1]);
    dsy = prtDataSetStandard('Observations', [1 0;2 2; 3 3]);
    % Compute distance
    distance = prtDistanceCityBlock(dsx,dsy)