/**
   * Function to perform LU decomposition on a given matrix.
   *
   * @param in matrix object
   * @return array of matrix blocks
   * @throws DMLRuntimeException if DMLRuntimeException occurs
   */
  private static MatrixBlock[] computeLU(MatrixObject in) throws DMLRuntimeException {
    if (in.getNumRows() != in.getNumColumns()) {
      throw new DMLRuntimeException(
          "LU Decomposition can only be done on a square matrix. Input matrix is rectangular (rows="
              + in.getNumRows()
              + ", cols="
              + in.getNumColumns()
              + ")");
    }

    Array2DRowRealMatrix matrixInput = DataConverter.convertToArray2DRowRealMatrix(in);

    // Perform LUP decomposition
    LUDecomposition ludecompose = new LUDecomposition(matrixInput);
    RealMatrix P = ludecompose.getP();
    RealMatrix L = ludecompose.getL();
    RealMatrix U = ludecompose.getU();

    // Read the results into native format
    MatrixBlock mbP = DataConverter.convertToMatrixBlock(P.getData());
    MatrixBlock mbL = DataConverter.convertToMatrixBlock(L.getData());
    MatrixBlock mbU = DataConverter.convertToMatrixBlock(U.getData());

    return new MatrixBlock[] {mbP, mbL, mbU};
  }
 public AbstractConfirmatoryFactorAnalysisEstimator(
     ConfirmatoryFactorAnalysisModel model, RealMatrix varcov, double numberOfExaminees) {
   this.model = model;
   this.varcov = varcov;
   this.numberOfExaminees = numberOfExaminees;
   this.nItems = model.getNumberOfItems();
   LUDecomposition CVLUD = new LUDecomposition(varcov);
   VCinv = CVLUD.getSolver().getInverse();
 }