int idx1 = 0;
            int idx2;
            int _i;
            int _j;
            for (int i = 0; i < beta.length; i++) {
                _i = newIndices[i];
                for (int j = 0; j <= i; j++, idx1++) {
                    _j = newIndices[j];
                    if (_i > _j) {
                        idx2 = _i * (_i + 1) / 2 + _j;
                    } else {
                        idx2 = _j * (_j + 1) / 2 + _i;
                    }
                    covNew[idx1] = cov[idx2];
                }
            }
            return new RegressionResults(
                    betaNew, new double[][]{covNew}, true, this.nobs, rnk,
                    this.sumy, this.sumsqy, this.sserr, this.hasIntercept, false);
        }
    }

public double chiSquare(final double[] expected, final long[] observed)
        throws MathIllegalArgumentException {

        if (expected.length < 2) {
            throw new MathIllegalArgumentException(LocalizedCoreFormats.DIMENSIONS_MISMATCH,
                                                   expected.length, 2);
        }
        MathUtils.checkDimension(expected.length, observed.length);
        MathArrays.checkPositive(expected);
        MathArrays.checkNonNegative(observed);

        double sumExpected = 0d;
        double sumObserved = 0d;
        for (int i = 0; i < observed.length; i++) {
            sumExpected += expected[i];
            sumObserved += observed[i];
        }
        double ratio = 1.0d;

int nVars = matrix.getColumnDimension();
        RealMatrix outMatrix = new BlockRealMatrix(nVars, nVars);
        for (int i = 0; i < nVars; i++) {
            for (int j = 0; j < i; j++) {
                double corr = correlation(matrix.getColumn(i), matrix.getColumn(j));
                outMatrix.setEntry(i, j, corr);
                outMatrix.setEntry(j, i, corr);
            }
            outMatrix.setEntry(i, i, 1d);
        }
        return outMatrix;
    }

    /**
     * Computes the Kendall's Tau rank correlation matrix for the columns of
     * the input rectangular array.  The columns of the array represent values
     * of variables to be correlated.
     *
     * @param matrix matrix with columns representing variables to correlate
     * @return correlation matrix
     */
    public RealMatrix computeCorrelationMatrix(final double[][] matrix) {