### matrix operations

I am new to SAGE. I need to create a matrix by using matrices of different sizes. For example:

Abar= [(A + B), C]

```
[ D , E]
```

where A and B are 2x2's, C is a 2x1, D is a 1x2, and E is a 1x1. I do not need Abar to be a partitioned matrix. Thanks much.