dcgain on discrete-time systems is wrong #114
Description
dcgain should distinguish between continuous- and discrete-time systems when determining DC gain.
import control
gct=control.tf([1],[1,1])
gcs=control.ss(gct)
gdt=control.sample_system(gct,5e-2,method='zoh')
gds=control.ss(gdt)
print('gct.dcgain()',gct.dcgain())
print('gcs.dcgain()',gcs.dcgain())
print('gdt.dcgain()',gdt.dcgain())
print('gds.dcgain()',gds.dcgain())
print('gdt.horner(1)',gdt.horner(1))
print('gds.horner(1)',gds.horner(1))gives
gct.dcgain() 1.0
gcs.dcgain() 1.0
gdt.dcgain() -0.051271096376024033
gds.dcgain() -0.051271096376024033
gdt.horner(1) [[ 1.+0.j]]
gds.horner(1) [[ 1.]]