From 5e6a7ebf636d11a71e92883abc366e094f48e599 Mon Sep 17 00:00:00 2001
From: Fredrik Bagge Carlson <baggepinnen@gmail.com>
Date: Sat, 21 Aug 2021 08:03:35 +0200
Subject: [PATCH 1/2] optional epsilon in dcgain

---
 src/analysis.jl | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/analysis.jl b/src/analysis.jl
index 9b2a31931..1f10aaabd 100644
--- a/src/analysis.jl
+++ b/src/analysis.jl
@@ -89,13 +89,17 @@ function det(sys::Matrix{S}) where {S<:SisoZpk}
 end
 
 """
-    dcgain(sys)
+    dcgain(sys, ϵ=0)
 
 Compute the dcgain of system `sys`.
 
-equal to G(0) for continuous-time systems and G(1) for discrete-time systems."""
-function dcgain(sys::LTISystem)
-    return iscontinuous(sys) ? evalfr(sys, 0) : evalfr(sys, 1)
+equal to G(0) for continuous-time systems and G(1) for discrete-time systems.
+
+`ϵ` can be provided to evaluate the dcgain at a small
+non-zero frequency.
+"""
+function dcgain(sys::LTISystem, ϵ=0)
+    return iscontinuous(sys) ? evalfr(sys, -ϵ) : evalfr(sys, 1-ϵ)
 end
 
 """

From 365ec83fa51484b8554d17d6d377d88c349fc655 Mon Sep 17 00:00:00 2001
From: Fredrik Bagge Carlson <baggepinnen@gmail.com>
Date: Sat, 21 Aug 2021 08:24:51 +0200
Subject: [PATCH 2/2] Update analysis.jl

---
 src/analysis.jl | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/analysis.jl b/src/analysis.jl
index 1f10aaabd..d286d644b 100644
--- a/src/analysis.jl
+++ b/src/analysis.jl
@@ -95,11 +95,11 @@ Compute the dcgain of system `sys`.
 
 equal to G(0) for continuous-time systems and G(1) for discrete-time systems.
 
-`ϵ` can be provided to evaluate the dcgain at a small
-non-zero frequency.
+`ϵ` can be provided to evaluate the dcgain with a small perturbation into
+the stability region of the complex plane.
 """
 function dcgain(sys::LTISystem, ϵ=0)
-    return iscontinuous(sys) ? evalfr(sys, -ϵ) : evalfr(sys, 1-ϵ)
+    return iscontinuous(sys) ? evalfr(sys, -ϵ) : evalfr(sys, exp(-ϵ*G.Ts))
 end
 
 """