code: protected double[] modifyPriorVector(double P[], double u, Random r, boolean skew) {
          for (int j = 0; j < P.length; j++) {
              if (r.nextDouble() < u) {
                  P[j] = r.nextDouble();
              }
          }
          return P;
      }
docs: ModifyPriorVector. A certain number of values will be altered.
  
  @param	P[]	the prior distribution
  @param	u	the probability of changing P[j]
  @param	r	for random numbers
  @param	skew	NOTE not currently used
  @return	the modified P