Write a sum of equation in Wolfram Language?

[tadejkaferle (tomo2 //)]

Hello!
How can I program this equation in Mathematica?

I would really appreciate some help with this problem.

[gianlucagorni]

It depends on what you want to do with it. This is a way:

u = Sum[z[i, j] deltaI[j], {j, 1, n}]

[tadejkaferle (tomo2 //)]

thank you