code: public static float[] stddev (int[] values, int start, int length)
      {
          // first we need the mean
          float mean = 0f;
          for (int ii = start, end = start + length; ii < end; ii++) {
              mean += values[ii];
          }
          mean /= length;
  
          // next we compute the variance
          float variance = 0f;
          for (int ii = start, end = start + length; ii < end; ii++) {
              float value = values[ii] - mean;
              variance += value * value;
          }
          variance /= (length - 1);
  
          // the standard deviation is the square root of the variance
          return new float[] { mean, variance, (float)Math.sqrt(variance) };
      }
docs: Computes the standard deviation of the supplied values.
  
  @return an array of three values: the mean, variance and standard deviation, in that order.