for (k in 2:length(tt)) { PV[k] = pv(PV[k-1], U[k-1], tt[k]) E[k] = PV[k] - SP[k] EI[k] = EI[k-1] + E[k]*dt # integral ED[k] = (E[k] - E[k-1])/dt # derivative U[k] = Kp*(E[k] + (1/Ti)*sum(E*dt) + Td*ED[k]) if (U[k] < 0) U[k] = 0 }