Inner product with homomorphic encryption I want to do a very simple thing: Given two vectors, I want to encrypt them and do some calculation, then decrypt the result and get the inner product between both vectors. I want to do this as fast as possible for the biggest vector dimension possible. 

Can you recommend any reference which may help me understand things and how to do it?

Or maybe you can even point me to some library that can do this? I found HELIB, but I don´t know if that is the best solution for my purpose. Since I have only basic knowledge in cryptography, I´ld like use it as black box as much as possible without having to put too much effort in the math behind it.
You can use these schemes instead: 


“Evaluating 2-DNF Formulas on Ciphertexts”, or
“A Simple BGN-type Cryptosystem from LWE”.


These schemes enable you to do addition, a single multiplication, and more additions. For inner product, that's all you need (encrypt each item separately, multiply pairs, and add all together).

Not everything needs FHE. In any case, somewhat HE would suffice since it's just a single multiplication.