[R] unable to plot bode - phase with control package

[fr1d_mail]

Dear All

I hope my question is relevant on this forum, else very sorry for the 
disturbance

I want to simply plot a bode diagram of a siso model

using the 'bodeplot' command in the control package fail due to error in 
'issiso' evaluation...

Error in if (issiso(sys)) {:

then I try by myself some retro-engineering :)

the problem is when I use

H <- freqresp(syst, w)
mag = 20*log10(abs(H))
phase <- atan2(Im(H), Re(H)) * 180/pi

if the order of the system is higher than 2 it is wrong (result will be 
only between -pi / pi)

how to proceed ? for each evaluated point take a derivative and evaluate 
the order to add the proper number of pi ?

Thanks for the help !

Best

Frédéric