docs: private double getHalfLogDeterminant(CholeskyDecomposition chol) {
      double[][] l = chol.getL();
      double logdet = FastMath.log(l[0][0]);
      for(int i = 1; i < l.length; i++) {
        // We get half the log(det), because we did not square values here.
        logdet += FastMath.log(l[i][i]);
      }
      return logdet;
    }