• In control dynamics u have a transfer function and need to determine the Routh-Hurwitz criterion it will sometimes give u division by 0 errors so u sub in a variable and say its almost zero but not quite and continue on like nothing happened.

      Eg determining the stability of a system with characteristic eq of A(s) = 3s4+6s3+2s^2+4s+5=0

      If u do a RH array u will end up with a zero which then will give u (4*0−30)/0 so u sub in 𝜀 for 0 giving (4𝜀−30)/𝜀 and continue on. That eq obviously evaluates to negative infinity. U are essentially just saying 𝜀 is an infinity small positive number ie it is the number next to 0 on the positive side.

      EDIT: If the markdown is messed up the eq should be A(s) = 3s**4+6s**3+2s**2+4s+5=0

      When using ** as super notation