Perform Popov robust stability test
[t,P,S,N] = popov(sys,delta,flag)
popov uses the Popov criterion to test the robust stability of dynamical systems with possibly nonlinear and/or time-varying uncertainty. The uncertain system must be described as the interconnection of a nominal LTI system sys and some uncertainty delta.
The command
[t,P,S,N] = popov(sys,delta)
tests the robust stability of this interconnection. Robust stability is guaranteed if t < 0. Then P determines the quadratic part xTPx of the Lyapunov function and D and S are the Popov multipliers.
If the uncertainty delta contains real parameter blocks, the conservatism of the Popov criterion can be reduced by first performing a simple loop transformation. To use this refined test, call popov with the syntax
[t,P,S,N] = popov(sys,delta,1)