Didn't get the difference formula written in question

#1

∑ i = 1 N / 2 a b s ( A i − B i )
, What does this means, I didn’t get this

#2

@Akshay123,
It means |A_1-B_1| + |A_2-B_2| + |A_3-B_3| ...... + |A_j-B_j| ,where j = N/2

#3

Thanks man, very helpful