zpkdata implementation flawed when considering discrete systems

[mfalt]

From @baggepinnen on February 27, 2016 9:47

The code below, is wrong, both for continuous and discrete systems

function _zpk_kern(s::SisoRational)
  return roots(s.num), roots(s.den), s.num[1]/s.den[1]
end

this fix works for continuous

function _zpk_kern(s::SisoRational)
  return roots(s.num), roots(s.den), s.num[end]/s.den[end]
end

but not for discrete, since SisoRational does not hold info regarding cont/discrete

Copied from original issue: mfalt/Control.jl#28

[mfalt]

From @baggepinnen on February 27, 2016 11:54

mostly fixed in pid branch

[mfalt]

How do you define the k in discrete time? I thought it would still be k*(z^n+b1z^{n-1}...bn)/(z^n+a1z^{n-1}...an).