1 | initial version |

I'm not sure what you've tried, but you need to convert the vectors to matrices:

```
sage: A = matrix([[1, 2, 3, 4],[4, 3, 2, 1],[2, 4, 3, 1]])
sage: II = identity_matrix(3)
sage: b = vector([10, 20, 30])
sage: c = vector([1, -2, 3, -1])
sage: z = zero_vector(3) # use a vector with 3 entries, for consistency with the size of II
sage: m = block_matrix(2, [[A, II, matrix(b).transpose()], [matrix(c), matrix(z), zero_matrix(1, 1)]])
sage: m
[ 1 2 3 4| 1 0 0|10]
[ 4 3 2 1| 0 1 0|20]
[ 2 4 3 1| 0 0 1|30]
[-----------+--------+--]
[ 1 -2 3 -1| 0 0 0| 0]
```

Now you can modify the subdivisions, if you don't like the current ones. For example:

```
sage: m.subdivisions() # current subdivision
([3], [4, 7])
sage: m.subdivide([3], [7])
sage: m
[ 1 2 3 4 1 0 0|10]
[ 4 3 2 1 0 1 0|20]
[ 2 4 3 1 0 0 1|30]
[--------------------+--]
[ 1 -2 3 -1 0 0 0| 0]
```

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