Merge branch 'master' into scalar_u

Author: baggepinnen

src/analysis.jl

@@ -464,7 +464,7 @@ Given a transfer function describing the Plant `P` and a transferfunction descri
 `T = PC/(1+PC)` Complementary sensitivity function
 
 Only supports SISO systems"""
-function gangoffour(P::TransferFunction,C::TransferFunction)
+function gangoffour(P::LTISystem,C::LTISystem)
     if P.nu + P.ny + C.nu + C.ny > 4
         error("gangoffour only supports SISO systems")
     end

src/freqresp.jl

@@ -39,14 +39,19 @@ function _preprocess_for_freqresp(sys::StateSpace)
 end
 
 
+function _evalfr_return_type(sys::StateSpace{<:TimeEvolution,T0}, s::Number) where {T0}
+    temp_product = one(T0)*one(typeof(s))
+    typeof(temp_product/temp_product)
+end
+
 """
 `evalfr(sys, x)` Evaluate the transfer function of the LTI system sys
 at the complex number s=x (continuous-time) or z=x (discrete-time).
 
 For many values of `x`, use `freqresp` instead.
 """
 function evalfr(sys::StateSpace{<:TimeEvolution,T0}, s::Number) where {T0}
-    T = promote_type(T0, typeof(one(T0)*one(typeof(s))/(one(T0)*one(typeof(s)))))
+    T = _evalfr_return_type(sys, s)
     try
         R = s*I - sys.A
         sys.D + sys.C*((R\sys.B)::Matrix{T})  # Weird type stability issue

test/test_pid_design.jl

@@ -3,6 +3,7 @@
 
 P = tf(1,[1,1])^4
 gangoffourplot(P,tf(1))
+gangoffourplot(ss(P),ss(1))
 ωp = 0.8
 kp,ki,C = loopshapingPI(P,ωp,phasemargin=60, doplot=true)
 @test kp ≈ 0.82274734724854