[Scilab-users] Something wrong with the conversion from frequency domain to time domain? Classic List Threaded 1 message  Hello, I'm trying to convert a function from continuous time to discrete time. There is following continuous time transfer function. Gc = 1 / (1 + 0.1*s) I converted to continuous time state space. Gsl = tf2ss(Gc) and converted to discrete time state space with dt = 0.001 sec. Gsd = dscr(Gsl, 0.001) Finally, converted to discrete time transfer function. Gd = ss2tf(Gsd) The result is following: Gd  =       0.0099502     ---------------     -0.9900498 + z I converted these function with the inverse Laplace transform and the inverse z transform. Inverse Laplace transform: L^-1[Gc] = y(t) = 10*e^(-10*t) Inverse Z transform: Apply 'z^-1' to numerator and denominator. Z^-1[Gd] = 0.0099502 * z^-1 / (-0.9900498 * z^-1 + 1) Apply the inverse z transform formula 'L^-1[1/(1 - az)] = a^n * u[n]' and 'L^-1[z^-k * F] = D^k * F'. Z^-1[Gd] = 0.0099502 * D^-1 * 0.9900498^n * u[n];      y[n] = 0.0099502 * 0.9900498^[n-1] * u[n]; I calculated these expressions in Excel. t    y(t)        y[n] 0    10          0.0099502 1    9.900498337 0.0099502 2    9.801986733 0.009851194 3    9.704455335 0.009753172 4    9.607894392 0.009656126 5    9.512294245 0.009560046 6    9.417645336 0.009464921 7    9.323938199 0.009370744 8    9.231163464 0.009277503 9    9.139311853 0.00918519 The numerical value is greatly different. Did I mistake something? Thanks in advance. moi _______________________________________________ users mailing list [hidden email] http://lists.scilab.org/mailman/listinfo/users