Notation relevant to Chapter 4

 A, A(s)  actuator transfer function
 A, A(s)  even part of (s)
 A(j) = Re (j)
 Ao  maximum available feedback
 A  value of A at s =
 B, B(s)  feedback path transfer function
 B, B(s)  odd part of (s)
 B(j) = Im (j)
 Bn  nonminimal phase lag
 C, C(s)  compensator transfer function
 F = T + 1  return difference
 |F|, or, also, 20 log|F|  feedback
 M = T/F  tracking system transmission coefficient
 NA  noise at the actuator input
 P, P(s)  plant transfer function
 R, R(s)  prefilter transfer function
 S  sensitivity
 T  return ratio, or loop transmission coefficient (T = CAPB)
 f  frequency in Hz
 fb  frequency at which loop gain is 0 dB
 fc  lowest frequency at which loop gain is -x dB
 fd  highest frequency at which loop gain is -x dB
 fg  lowest frequency at which loop gain is x1 dB
 fh  highest frequency at which loop gain is x1 dB
 fp, fz  frequencies of a pole, of a zero
 k  motor constant
 k  coefficient
 n  slope coefficient of an asymptotic Bode diagram
 s = + j  operational variable
 t  time
 td, tr, ts  delay, rise, and settling times
 u, u(t)  signal at system's input, command
 x  lower amplitude stability margin in dB
 x1  upper amplitude stability margin in dB
 y, or y  phase stability margin
 , (s), (j)  transfer function
   angle of rotation
   torque
  = 1/(2Q)  damping coefficient
   frequency, rad/sec