make time responses of tf use minimal realization

Author: baggepinnen

lib/ControlSystemsBase/src/timeresp.jl

@@ -71,7 +71,7 @@ end
 
 Base.step(sys::LTISystem, tfinal::Real; kwargs...) = step(sys, _default_time_vector(sys, tfinal); kwargs...)
 Base.step(sys::LTISystem; kwargs...) = step(sys, _default_time_vector(sys); kwargs...)
-Base.step(sys::TransferFunction, t::AbstractVector; kwargs...) = step(ss(sys), t::AbstractVector; kwargs...)
+Base.step(sys::TransferFunction, t::AbstractVector; kwargs...) = step(ss(sys, balance=true, minimal=true), t::AbstractVector; kwargs...)
 
 """
     y, t, x = impulse(sys[, tfinal])
@@ -119,7 +119,7 @@ end
 
 impulse(sys::LTISystem, tfinal::Real; kwargs...) = impulse(sys, _default_time_vector(sys, tfinal); kwargs...)
 impulse(sys::LTISystem; kwargs...) = impulse(sys, _default_time_vector(sys); kwargs...)
-impulse(sys::TransferFunction, t::AbstractVector; kwargs...) = impulse(ss(sys), t; kwargs...)
+impulse(sys::TransferFunction, t::AbstractVector; kwargs...) = impulse(ss(sys, balance=true, minimal=true), t; kwargs...)
 
 """
     result = lsim(sys, u[, t]; x0, method])
@@ -301,7 +301,7 @@ function lsim(sys::AbstractStateSpace, u::Function, t::AbstractVector;
 end
 
 
-lsim(sys::TransferFunction, args...; kwargs...) = lsim(ss(sys), args...; kwargs...)
+lsim(sys::TransferFunction, args...; kwargs...) = lsim(ss(sys, balance=true, minimal=true), args...; kwargs...)
 
 
 """

test/test_timeresp.jl

@@ -75,7 +75,7 @@ xreal[3,:,2] = exp.(-t).*t
 y, t, x = step(systf, t0, method=:zoh)
 yreal[1,:,1] = 1 .- exp.(-t)
 yreal[2,:,2] = -1 .+ exp.(-t) + 2*exp.(-t).*t
-@test y ≈ yreal atol=1e-14
+@test y ≈ yreal atol=1e-13
 #Step ss
 y, t, x = step(sysss, t, method=:zoh)
 @test y ≈ yreal atol=1e-13
@@ -88,7 +88,7 @@ xreal[3,:,2] = exp.(-t).*(-t .- 1) .+ 1
 y, t, x = impulse(systf, t, method=:zoh)
 yreal[1,:,1] = exp.(-t)
 yreal[2,:,2] = exp.(-t).*(1 .- 2*t)
-@test y ≈ yreal atol=1e-14
+@test y ≈ yreal atol=1e-13
 #Impulse ss
 y, t, x = impulse(1.0sysss, t, method=:zoh)
 @test y ≈ yreal atol=1e-13