docs: public static void applyHouseholder(DMatrixSparseCSC V , int colV, double beta ,
                                          double []x) {
          int idx0 = V.col_idx[colV];
          int idx1 = V.col_idx[colV+1];
  
          // Compute tau = v'*x
          double tau = 0;
          for (int p = idx0; p < idx1; p++) {
              tau += V.nz_values[p]*x[V.nz_rows[p]];
          }
          tau *= beta;
  
          // x = x - v*tau
          for (int p = idx0; p < idx1; p++) {
              x[V.nz_rows[p]] -= V.nz_values[p]*tau;
          }
      }