+ ∑ m ˜ wim + ∑ n ˜ wni ˜ wb ij = ∑ k wb ijk ˜ we ij = λe ij ⋅ ∑ k we ijk wb ijk = μk ⋅ λb ij we ijk = min ( 1, δe ijk 30 ) λb ijk = exp (ln(CPy ⋅ 365 / δb ijk ) ⋅ (1 − γij ) ⋅ Δγ) − 1 λe ij = exp (ln(CPy ⋅ 365 / δe ij ) ⋅ (1 − γe) ⋅ Δγ) − 1 μk = { ln(priceb k ) (if 0 < priceb k AND bk is sent) priceb k (if 0 < priceb k AND bk is received) γij = { σij (1 / rsij ) (if CPd < δb k ) 0 (otherwise) δb ijk = ⌊ tcurrent − tb ijk 86400 ⌋ − CPd (if 0 < δb k ) 1 (otherwise) δe ij = ⌊ tcurrent − te ij 86400 ⌋ − CPd (if 0 < δe ij ) 1 (otherwise) δe ijk = ⌊ te ijk − te ij(k−1) 86400 ⌋ (if 1 < k) ⌊ tcurrent − te ijk 86400 ⌋ (otherwise) rsij = ̂ εij + B ⋅ ̂ kij δe ij σij (x) = tanh ( x x + 1 ) bsi : bajji score of Ai (Ai : accounti ) rsij : relationship score between Ai and Aj B : bajji constant (B = 8.8) CPy : bajji critical point year (CPy = B) CPd : bajji critical point date (CPd = 10B) Δγ : Aging correction (Δγ = B/1,000) ̂ uεi : Number of encounters between Ai and unique users ̂ ug i : Number of bajjis sent from Ai to unique users ̂ uri : Number of bajjis received by Ai from unique users ̂ εi : Number of encounters between Ai and users ̂ gi : Number of bajjis sent from Ai to users ̂ ri : Number of bajjis received by Ai from users ˜ wij : Sum of the value of the bajji sent from Ai to Aj wijk : Value of the bajjik sent from Ai to Aj priceb k : Price of the bajjik tcurrent : Current datetime [sec] ̂ εij : Number of encounter between Ai and Aj ̂ kij : Number of bajji send Ai to Aj tb k : Datetime of the bajjik sent and received [sec] te ij : Datetime of the last encounter between Ai and Aj [sec] γe : Aging rate of encounter (γe = 0.0) γij : Aging rate between Ai and Aj δb k : Difference of days since the bajjik sent and received between Ai and Aj δe ij : Difference of days since the last encountered between Ai and Aj