Gradient of vector-valued function

Code below throws an error. How is it possible to get the gradient for a vector-valued function?

syms a b1 b2 t
mfcn = matlabFunction(b1.*t^2+b2.*t, 'Vars', {[b1,b2],t})
gradient(mfcn,t)

Answer 1

[Moritz Schulze]

syms a b1 b2 t
mfcn = matlabFunction(b1.*t^2+b2.*t)
gradient(mfcn,t)

This works on the contrary.

Answer 2

[VBBV]

use diff instead of gradient which is equivalent for gradient operation for symbolic expressions

syms a b1 b2 t
mfcn = matlabFunction(b1.*t.^2+b2.*t,'Vars', {b1,b2,t})

mfcn = function_handle with value:
    @(b1,b2,t)b2.*t+b1.*t.^2

diff(mfcn,t)  % use diff instead of gradient 

ans =