code: public static void solveTranL(DMatrixSparseCSC L , double []x )
      {
          final int N = L.numCols;
  
          for (int j = N-1; j >= 0; j--) {
              int idx0 = L.col_idx[j];
              int idx1 = L.col_idx[j+1];
  
              for (int p = idx0+1; p < idx1; p++) {
                  x[j] -= L.nz_values[p]*x[L.nz_rows[p]];
              }
              x[j] /= L.nz_values[idx0];
          }
      }
docs: Solves for the transpose of a lower triangular matrix against a dense matrix. L<sup>T</sup>*x = b
  
  @param L Lower triangular matrix.  Diagonal elements are assumed to be non-zero
  @param x (Input) Solution matrix 'b'.  (Output) matrix 'x'