Optimization problem with summatory

Hello every one i have an exercise to do in matlab using fminsearch or fminunc, as you can see the function below, i have a variable between -5.12 and 5.12, Is there a method in matlab to declare a vector of functions which means every element of this vector is a variable, im asking this cause fminsearch i need to create a function in the form f=(v1,v2,v3) (2-D or 3-D) where v1,v2 and v3 are the variables and imply the dimention. The problem in my case is i need to expand the summatory between -5 to 5 and create the function expanded, instead of using a for. In other word can i use a for to do this? The derivative works for every xi as you can see.