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(ρV0−⌊ρV0+0.5⌋)2+(ρV1−⌊ρV1+0.5⌋)2+...+(ρVi−⌊ρVi+0.5⌋)2
let ki=⌊ρVi+0.5⌋ i∈[0,n]
=(ρV0−k0)2+(ρV1−k1)2+...+(ρVi−ki)2
=(ρ2V02−2ρk0V0+k02)+(ρ2V12−2ρk0V1+k12)+…+(ρ2Vi2−2ρkiVi+ki2)
=ρ2(V02+V12+…+Vi2)−2ρ(k0V0+k1V1+…+kiVi)+(k02+k12+…+ki2)
=ρ2∑i=0nVi2−2ρ∑i=0nkiVi+∑i=0nki2
let K=∑i=0nki2, V=∑i=0nVi2 i∈[0,n]
=ρ2V−2ρ∑i=0nkiVi+K