code: public static double[] rowStdDevs(RealMatrix matrix) {
          double[] retval = new double[matrix.getRowDimension()];
          for (int i = 0; i < retval.length; i++) {
              retval[i] = new DescriptiveStatistics(matrix.getRow(i)).getStandardDeviation();
          }
          return retval;
      }
docs: Returns the standard deviations of rows.
  
  @param matrix The matrix of which the standard deviations of rows to be computed
  @return A double array of row standard deviations.