code: public Matrix times(Matrix B) {
          Matrix A = this;
          if (A.N != B.M) {
              throw new RuntimeException("Illegal matrix dimensions.");
          }
          Matrix C = new Matrix(A.M, B.N);
          for (int i = 0; i < C.M; i++) {
              for (int j = 0; j < C.N; j++) {
                  for (int k = 0; k < A.N; k++) {
                      C.data[i][j] += A.data[i][k] * B.data[k][j];
                  }
              }
          }
          return C;
      }
docs: return C = A * B