MATLAB: Bad partial differentiation

Question

Hi, I've a problem with this:

input parameter to my function is degree-it's number

There is a reason why I need m0,phi0 and not l0

    m=sym('m',[1,degree]);
    m=[m0 m];
    l=sym('l',[degree,1]);
    phi=sym('phi',[1,degree]);
    phi=[phi0 phi] ;
    for i=1:length(phi)
        phi(i)=strcat(char(phi(i)),'(t)');
    end
    B=(1/2)*l(1)*m(2)*diff(phi(1),t)*diff(phi(2),t)*cos(phi(2))
    phit=phi(2)
    subs(diff(subs(B, phit, 'phit'),'phit'),'phit', phit)

I want to derive according to phi1(t), and the result is 0, but I expect (-1/2)*l1*m1*diff(phi0(t),t)*diff(phi1(t),t)*sin(phi1(t))

BUT, when I derive this B=(1/2)*l(1)*m(2)*diff(phi(1),t)*cos(phi(2)), it's all righ,

Any help would be appreciated

Answer 1

The MuPAD Symbolic Toolbox cannot differentiate with respect to a function. (Maple cannot either.)