# Sum of two vectors

Hi everybody, i've got this functions and variables:

```
v = function('v',t)
a_V_ra = function('a_V_ra',t)
a_a_ra=function('a_a_ra',t)
g = var('g')
r_V_ra = vector([v,0,0])
a_V_ra = R_ra*r_V_ra.column()
```

where R is a matrix and a_V_ra is the vector [cos(psi(t))v(t), sin(psi(t))v(t),0].

But when i do this:

```
a_a_ra = diff(a_V_ra)+vector([0,0,-g])
```

it says: *TypeError: unsupported operand parent(s) for '+': 'Full MatrixSpace of 3 by 1 dense matrices over Symbolic Ring' and 'Vector space of dimension 3 over Symbolic Ring'*

I guess it's saying that i'm summing a matrix and a vector, but they're both vectors! What can I do to make it work?

Thank you.