I just started using Eigen library and can't understand how to add a scalar value to all matrix's members?

Let's suppose that I have a matrix:

```cpp
Eigen::Matrix3Xf mtx = Eigen::Matrix3Xf::Ones(3,4);
mtx = mtx + 1;    // main.cxx:104:13: error: invalid operands to binary expression ('Eigen::Matrix3Xf' (aka 'Matrix<float, 3, Dynamic>') and 'int')

```

I expect that the resulting matrix would be filled with 2