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