Symbolic math, differentiate an equation wrt to element in a array

Hi folks,

I want to differentiate an equation with respect to a variable assigned in a vector.

where v is a 1*N vector, ie [x_r; y_r.....N] etc

     for i=1:1:size(v,1)
           SE_ans(i)= diff(SE,i) 
     end

I thought the above would work. Any help appreciated.