From d0ba23165b136c94c596c167acc8d03bfe06d782 Mon Sep 17 00:00:00 2001
From: Fredrik Bagge Carlson <baggepinnen@gmail.com>
Date: Sun, 17 Jan 2021 06:34:56 +0100
Subject: [PATCH] more robust gangoffour and gofplot

---
 src/analysis.jl | 29 +++++++++++++++++------------
 src/plotting.jl | 14 ++++++++------
 2 files changed, 25 insertions(+), 18 deletions(-)

diff --git a/src/analysis.jl b/src/analysis.jl
index 8c928e3ee..58fb09672 100644
--- a/src/analysis.jl
+++ b/src/analysis.jl
@@ -451,28 +451,33 @@ function delaymargin(G::LTISystem)
     dₘ
 end
 
+function robust_minreal(G, args...; kwargs...)
+    try 
+        return minreal(G, args...; kwargs...)
+    catch
+        return G
+    end
+end
+
 """
     S,D,N,T = gangoffour(P,C; minimal=true)
     gangoffour(P::AbstractVector,C::AbstractVector; minimal=true)
-
+    
 Given a transfer function describing the Plant `P` and a transfer function describing the controller `C`, computes the four transfer functions in the Gang-of-Four.
 
-`minimal` determines whether or not to call `minreal` on the computed systems.
-
-`S = 1/(1+PC)` Sensitivity function
-
-`D = P/(1+PC)`
-
-`N = C/(1+PC)`
+- `minimal` determines whether or not to call `minreal` on the computed systems.
+- `S = 1/(1+PC)` Sensitivity function
+- `D = P/(1+PC)`
+- `N = C/(1+PC)`
+- `T = PC/(1+PC)` Complementary sensitivity function
 
-`T = PC/(1+PC)` Complementary sensitivity function
-
-Only supports SISO systems"""
+Only supports SISO systems
+"""
 function gangoffour(P::LTISystem,C::LTISystem; minimal=true)
     if P.nu + P.ny + C.nu + C.ny > 4
         error("gangoffour only supports SISO systems")
     end
-    minfun = minimal ? minreal : identity
+    minfun = minimal ? robust_minreal : identity
     S = (1/(1+P*C)) |> minfun
     D = (P*S)       |> minfun
     N = (C*S)       |> minfun
diff --git a/src/plotting.jl b/src/plotting.jl
index 787cf4be2..2c2c30aab 100644
--- a/src/plotting.jl
+++ b/src/plotting.jl
@@ -727,18 +727,20 @@ end
 pzmap(sys::LTISystem; kwargs...) = pzmap([sys]; kwargs...)
 pzmap!(sys::LTISystem; kwargs...) = pzmap!([sys]; kwargs...)
 
-"""`fig = gangoffourplot(P::LTISystem, C::LTISystem)`, `gangoffourplot(P::Union{Vector, LTISystem}, C::Vector; plotphase=false)`
-
-Gang-of-Four plot.
+"""
+    fig = gangoffourplot(P::LTISystem, C::LTISystem; minimal=true, plotphase=false, kwargs...)
+    gangoffourplot(P::Union{Vector, LTISystem}, C::Vector; minimal=true, plotphase=false, kwargs...)
 
-`kwargs` is sent as argument to Plots.plot."""
-function gangoffourplot(P::Union{Vector, LTISystem}, C::Vector, args...; plotphase=false, kwargs...)
+Gang-of-Four plot. `kwargs` is sent as argument to Plots.plot.
+"""
+function gangoffourplot(P::Union{Vector, LTISystem}, C::Vector, args...; minimal=true, plotphase=false, kwargs...)
     # Array of (S,D,N,T)
     if P isa LTISystem # Don't broadcast over scalar (with size?)
         P = [P]
     end
-    sys = gangoffour.(P,C)
+    sys = gangoffour.(P,C; minimal=minimal)
     fig = bodeplot([[sys[i][1] sys[i][2]; sys[i][3] sys[i][4]] for i = 1:length(C)], args..., plotphase=plotphase; kwargs...)
+    hline!([1 1 1 1], l=(:black, :dash), primary=false)
     titles = fill("", 1, plotphase ? 8 : 4)
     # Empty titles on phase
     titleIdx = plotphase ? [1,2,5,6] : [1,2,3,4]