Hi Dia Ghosh,

It is much easier to help you if you post the Mathematica code that you tried. For instance, the following command should works for me without any trouble:

tf = TransferFunctionModel[(Exp[s T] s)/(K + k s) /. {T -> 0.1, K -> 2, k -> 0.3}, s]
NyquistPlot[tf, {0.01, 100}]

But without knowing what code you used, it is impossible to help give a more exact answer. Things to consider though:

• The Nyquist plot function takes a transfer function or a state space model as an argument. These are generated using the TransferFunctionModel and StateSpaceModel functions.
• When you write sT and ks, Mathematica will interpret them as separate variables ("sT" and "ks"), not the multiplication of s and T etc. For that, you either need to use the multiplication operator or separate them by as space as I did above.

Patrik