Control Toolbox Function : zpk

[Richard Shadbolt]

Hi,

I am attempting to use the Control Toolbox function zpk which is stated 
to have been implemented :

https://wiki.octave.org/wiki/index.php?title=Control_package&mobileaction=toggle_view_desktop

Yet i am obtaining the error for a basic command :

    F=zpk([], [-1 -2 -2], 2);

The error is :

    error: '__lti_input_idx__' undefined near line 80 column 24

I think i am using the correct syntax etc.m for the command. The 
documentation page indicates that it may not be fully implemented.

    https://octave.sourceforge.io/control/function/zpk.html

States :

    Create transfer function model from zero-pole-gain data. This is 
just a stop-gap compatibility wrapper since zpk models are not yet 
implemented.

As such, can someone confirm whether the function has or has not been 
implemented ?

Thanks and regards,

Richard.