From 36a9350296e5b40264ee4180a0e7bda365504e08 Mon Sep 17 00:00:00 2001
From: Fredrik Bagge Carlson <baggepinnen@gmail.com>
Date: Mon, 9 Sep 2024 13:07:08 +0200
Subject: [PATCH] add function that resets the internal state

---
 Project.toml        |  2 +-
 README.md           |  2 ++
 src/DiscretePIDs.jl | 12 +++++++++++-
 test/runtests.jl    |  4 ++++
 4 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Project.toml b/Project.toml
index 68b5f0d..45761e0 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "DiscretePIDs"
 uuid = "c1363496-6848-4723-8758-079b737f6baf"
 authors = ["Fredrik Bagge Carlson"]
-version = "0.1.4"
+version = "0.1.5"
 
 [deps]
 Printf = "de0858da-6303-5e67-8744-51eddeeeb8d7"
diff --git a/README.md b/README.md
index 340edbc..bb7b38b 100644
--- a/README.md
+++ b/README.md
@@ -37,6 +37,8 @@ The parameters $K, T_i, T_d$ may be updated using the functions, `set_K!, set_Ti
 
 The numeric type used by the controller (the `T` in `DiscretePID{T}`) is determined by the types of the parameters. To use a custom number type, e.g., a fixed-point number type, simply pass the parameters as that type, see example below. The controller will automatically convert measurements and references to this type before performing the control calculations.
 
+The **internal state** of the controller can be reset to zero using the function `reset_state!(pid)`. If repeated simulations using the same controller object are performed, the state should likely be reset between simulations.
+
 ## Example using ControlSystems:
 The following example simulates the PID controller using ControlSystems.jl. We will simulate a load disturbance $d(t) = 1$ entering on the process input, while the reference is $r(t) = 0$.
 
diff --git a/src/DiscretePIDs.jl b/src/DiscretePIDs.jl
index f660281..06f9ff9 100644
--- a/src/DiscretePIDs.jl
+++ b/src/DiscretePIDs.jl
@@ -1,6 +1,6 @@
 module DiscretePIDs
 
-export DiscretePID, calculate_control!, set_K!, set_Td!, set_Ti!
+export DiscretePID, calculate_control!, set_K!, set_Td!, set_Ti!, reset_state!
 
 using Printf
 
@@ -184,5 +184,15 @@ function Base.show(io::IO, ::MIME"text/plain", pid::DiscretePID)
     println(io, ")")
 end
 
+"""
+    reset_state!(pid::DiscretePID)
+
+Set all internal state variables to zero (`I`, `D` and `yold`).
+"""
+function reset_state!(pid::DiscretePID)
+    pid.I = zero(pid.I)
+    pid.D = zero(pid.D)
+    pid.yold = zero(pid.yold)
+end
 
 end
diff --git a/test/runtests.jl b/test/runtests.jl
index b79db35..904bb45 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -91,6 +91,10 @@ res2 = lsim(P, ctrl, Tf)
 @test res.y ≈ res2.y rtol=0.02
 # plot([res, res2])
 
+reset_state!(pid)
+res3 = lsim(P, ctrl, Tf)
+@test res3.y == res2.y
+
 ## Test with FixedPointNumbers
 using FixedPointNumbers
 T = Fixed{Int16, 10} # 16-bit signed fixed-point with 10 bits for the fractional part