Summing function Wm(time,a,b,c,d) from m=0 to m=n ?

To all,

I am sure I saw something about how to do such thing but I cannot find it so needs some pointers

I have a function (see attached mcad sheet) Wm(t,am,bm,cm,dm) where t is time and a_m,b_m,c_m,d_m are coefficient valid for equation m

I need to do sum of W_m from m =0 to n:      but I am struggling with indices in mcad

Coudl anyone refreshe my memory on this summation? It might be something with "dicretizing" the time 't' if I recall

Thanks

Regards

JXB