Why am I unable to change the values for damping ratio in the "Edit Compensator" GUI using SISOTOOL in the Control System Toolbox?

I created a model in SISOTOOL, and am attempting to modify the poles and zeros of a compensator using the "Compensators -> Edit" GUI. Some or all of the poles and zeros were initially specified as real poles/zeros. When I change the "Format" to "Damping Ratio/Natural Frequency", I am unable to edit the damping ratios of some poles and zeros.

Answer 1

[MathWorks Support Team]

This enhancement has been incorporated in Release 2006a (R2006a). For previous product releases, read below for any possible workarounds:

The ability to change poles and zeros from real to complex by modifying the "Damping Ratio" field is not available in the Control System Toolbox.

This behavior occurs because poles and zeros initially specified as real poles/zeros remain real and cannot be changed to complex poles by editing the "Damping Ratio" field.

To work around this issue, delete the real pole or zero and add a new complex pole or zero.