code: public static double correlation( TupleDesc_F64 a, TupleDesc_F64 b) {
  		final int N = a.value.length;
  		double total = 0;
  		for( int i = 0; i < N; i++ ) {
  			total += a.value[i]*b.value[i];
  		}
  
  		return total;
  	}
docs: Correlation score
  
  @param a First descriptor
  @param b Second descriptor
  @return Correlation score