docs: public Matrix getD () {
        Matrix X = MatrixFactory.createMatrix(n,n);
        for (int i = 0; i < n; i++) {
           X.set(i,i,d[i]);
           if (e[i] > 0) {
  				X.set(i,i+1,e[i]);
           } else if (e[i] < 0) {
  				X.set(i,i-1,e[i]);
           }
        }
        return X;
     }