Given three vectors, `a`

(1,4), `b`

(1, 4), `c`

(4,1). I want to do the following

```
a = MatrixSymbol('a', 1, 4)
b = MatrixSymbol('a', 1, 4)
c = MatrixSymbol('c', 4, 1)
expr = a*c + b*c
c_coeff = .... # How to get the value of (a+b) here
```

I tried using `coeff`

and `collect`

but it fails because the C matrix is not square.

### >Solution :

If it is linear then

```
>>> from sympy.solvers.solveset import linear_coeffs
>>> linear_coeffs(expr, c)
[a + b, 0]
```

note that 0 is the constant term; if you added `MatrixSymbol('d', 1, 1)`

to `expr`

the 2nd element would be `d`

; you named ‘b’ as ‘a’ in your example; I named it ‘b’ to get the output shown above.