From 3985596609348daecc7f2453bcbd00823000ab48 Mon Sep 17 00:00:00 2001
From: Venkateshprasad <32921645+ven-k@users.noreply.github.com>
Date: Mon, 3 Jul 2023 12:40:48 +0530
Subject: [PATCH 1/7] refactor: Blocks/math.jl

---
 src/Blocks/analysis_points.jl       |   2 +-
 src/Blocks/math.jl                  | 240 +++++++++++++++-------------
 test/Blocks/math.jl                 |  10 +-
 test/Blocks/test_analysis_points.jl |   6 +-
 4 files changed, 141 insertions(+), 117 deletions(-)

diff --git a/src/Blocks/analysis_points.jl b/src/Blocks/analysis_points.jl
index bc3234e9b..a6b90866d 100644
--- a/src/Blocks/analysis_points.jl
+++ b/src/Blocks/analysis_points.jl
@@ -46,7 +46,7 @@ See also [`get_sensitivity`](@ref), [`get_comp_sensitivity`](@ref), [`get_looptr
 ```julia
 using ModelingToolkitStandardLibrary.Blocks
 @named P = FirstOrder(k = 1, T = 1)
-@named C = Gain(-1)
+@named C = Gain(; k = -1)
 t = ModelingToolkit.get_iv(P)
 eqs = [connect(P.output, C.input)
        connect(C.output, :plant_input, P.input)]
diff --git a/src/Blocks/math.jl b/src/Blocks/math.jl
index b3858a66d..f70c34e04 100644
--- a/src/Blocks/math.jl
+++ b/src/Blocks/math.jl
@@ -1,5 +1,5 @@
 """
-    Gain(k; name)
+    Gain(; name, k)
 
 Output the product of a gain value with the input signal.
 
@@ -12,15 +12,16 @@ Output the product of a gain value with the input signal.
   - `input`
   - `output`
 """
-@component function Gain(k; name)
-    @named siso = SISO()
-    @unpack u, y = siso
-    pars = @parameters k=k [description = "Gain of Gain $name"]
-    eqs = [
-        y ~ k * u,
-    ]
-    extend(ODESystem(eqs, t, [], pars; name = name), siso)
+@mtkmodel Gain begin
+    @extend u, y = siso = SISO()
+    @parameters begin
+        k, [description = "Gain"]
+    end
+    @equations begin
+        y ~ k * u
+    end
 end
+Gain.f(k; name) = Gain.f(; k, name)
 
 """
     MatrixGain(K::AbstractArray; name)
@@ -36,39 +37,48 @@ Output the product of a gain matrix with the input signal vector.
   - `input`
   - `output`
 """
-@component function MatrixGain(K::AbstractArray; name)
-    nout, nin = size(K, 1), size(K, 2)
-    @named input = RealInput(; nin = nin)
-    @named output = RealOutput(; nout = nout)
-    eqs = [output.u[i] ~ sum(K[i, j] * input.u[j] for j in 1:nin) for i in 1:nout]
-    compose(ODESystem(eqs, t, [], []; name = name), [input, output])
+@mtkmodel MatrixGain begin
+    @parameters begin
+        K, [description = "Matrix gain"]
+    end
+    begin
+        nout = size(getdefault(K), 1)
+        nin = size(getdefault(K), 2)
+    end
+    @components begin
+        input = RealInput(; nin = size(K, 2))
+        output = RealOutput(; nout = size(K, 1))
+    end
+    @equations begin
+        [(@info i, j; output.u[i] ~ sum(getdefault(K)[i, j] * input.u[j])) for j in 1:nin
+         for i in 1:nout]...
+    end
 end
+MatrixGain.f(K; name) = MatrixGain.f(; name, K)
 
 """
-    Sum(n::Int; name)
+    Sum(; input.nin::Int, name)
 
 Output the sum of the elements of the input port vector.
-
-# Parameters:
-
-  - `n`: Input port dimension
+Input port dimension can be set with `input.nin`
 
 # Connectors:
 
   - `input`
   - `output`
 """
-@component function Sum(n::Int; name)
-    @named input = RealInput(; nin = n)
-    @named output = RealOutput()
-    eqs = [
-        output.u ~ sum(input.u),
-    ]
-    compose(ODESystem(eqs, t, [], []; name = name), [input, output])
+@mtkmodel Sum begin
+    @components begin
+        input = RealInput(; nin)
+        output = RealOutput()
+    end
+    @equations begin
+        output.u ~ sum(input.u)
+    end
 end
 
 """
-    Feedback(;name)
+    Feedback(; name)
 
 Output difference between reference input (input1) and feedback input (input2).
 
@@ -78,18 +88,19 @@ Output difference between reference input (input1) and feedback input (input2).
   - `input2`
   - `output`
 """
-@component function Feedback(; name)
-    @named input1 = RealInput()
-    @named input2 = RealInput()
-    @named output = RealOutput()
-    eqs = [
-        output.u ~ input1.u - input2.u,
-    ]
-    return compose(ODESystem(eqs, t, [], []; name = name), input1, input2, output)
+@mtkmodel Feedback begin
+    @components begin
+        input1 = RealInput()
+        input2 = RealInput()
+        output = RealOutput()
+    end
+    @equations begin
+        output.u ~ input1.u - input2.u
+    end
 end
 
 """
-    Add(;name, k1=1, k2=1)
+    Add(; name, k1 = 1, k2 = 1)
 
 Output the sum of the two scalar inputs.
 
@@ -104,20 +115,23 @@ Output the sum of the two scalar inputs.
   - `input2`
   - `output`
 """
-@component function Add(; name, k1 = 1, k2 = 1)
-    @named input1 = RealInput()
-    @named input2 = RealInput()
-    @named output = RealOutput()
-    pars = @parameters(k1=k1, [description = "Gain of Add $name input1"],
-        k2=k2, [description = "Gain of Add $name input2"],)
-    eqs = [
-        output.u ~ k1 * input1.u + k2 * input2.u,
-    ]
-    return compose(ODESystem(eqs, t, [], pars; name = name), input1, input2, output)
+@mtkmodel Add begin
+    @components begin
+        input1 = RealInput()
+        input2 = RealInput()
+        output = RealOutput()
+    end
+    @parameters begin
+        k1 = 1, [description = "Gain of Add input1"]
+        k2 = 1, [description = "Gain of Add input2"]
+    end
+    @equations begin
+        output.u ~ k1 * input1.u + k2 * input2.u
+    end
 end
 
 """
-    Add(;name, k1=1, k2=1,k3=1)
+    Add(; name, k1 = 1, k2 = 1, k3 = 1)
 
 Output the sum of the three scalar inputs.
 
@@ -134,22 +148,25 @@ Output the sum of the three scalar inputs.
   - `input3`
   - `output`
 """
-@component function Add3(; name, k1 = 1, k2 = 1, k3 = 1)
-    @named input1 = RealInput()
-    @named input2 = RealInput()
-    @named input3 = RealInput()
-    @named output = RealOutput()
-    pars = @parameters(k1=k1, [description = "Gain of Add $name input1"],
-        k2=k2, [description = "Gain of Add $name input2"],
-        k3=k3, [description = "Gain of Add $name input3"],)
-    eqs = [
-        output.u ~ k1 * input1.u + k2 * input2.u + k3 * input3.u,
-    ]
-    return compose(ODESystem(eqs, t, [], pars; name = name), input1, input2, input3, output)
+@mtkmodel Add3 begin
+    @components begin
+        input1 = RealInput()
+        input2 = RealInput()
+        input3 = RealInput()
+        output = RealOutput()
+    end
+    @parameters begin
+        k1 = 1, [description = "Gain of Add input1"]
+        k2 = 1, [description = "Gain of Add input2"]
+        k3 = 1, [description = "Gain of Add input3"]
+    end
+    @equations begin
+        output.u ~ k1 * input1.u + k2 * input2.u + k3 * input3.u
+    end
 end
 
 """
-    Product(;name)
+    Product(; name)
 
 Output product of the two inputs.
 
@@ -159,18 +176,19 @@ Output product of the two inputs.
   - `input2`
   - `output`
 """
-@component function Product(; name)
-    @named input1 = RealInput()
-    @named input2 = RealInput()
-    @named output = RealOutput()
-    eqs = [
-        output.u ~ input1.u * input2.u,
-    ]
-    return compose(ODESystem(eqs, t, [], []; name = name), input1, input2, output)
+@mtkmodel Product begin
+    @components begin
+        input1 = RealInput()
+        input2 = RealInput()
+        output = RealOutput()
+    end
+    @equations begin
+        output.u ~ input1.u * input2.u
+    end
 end
 
 """
-    Division(;name)
+    Division(; name)
 
 Output first input divided by second input.
 
@@ -180,18 +198,19 @@ Output first input divided by second input.
   - `input2`
   - `output`
 """
-@component function Division(; name)
-    @named input1 = RealInput()
-    @named input2 = RealInput(u_start = 1.0) # denominator can not be zero
-    @named output = RealOutput()
-    eqs = [
-        output.u ~ input1.u / input2.u,
-    ]
-    return compose(ODESystem(eqs, t, [], []; name = name), input1, input2, output)
+@mtkmodel Division begin
+    @components begin
+        input1 = RealInput()
+        input2 = RealInput(u_start = 1.0) # denominator can not be zero
+        output = RealOutput()
+    end
+    @equations begin
+        output.u ~ input1.u / input2.u
+    end
 end
 
 """
-    StaticNonLinearity(func ;name)
+    StaticNonLinearity(func; name)
 
 Applies the given function to the input.
 
@@ -202,15 +221,19 @@ If the given function is not composed of simple core methods (e.g. sin, abs, ...
   - `input`
   - `output`
 """
-@component function StaticNonLinearity(func; name)
-    @named siso = SISO()
-    @unpack u, y = siso
-    eqs = [y ~ func(u)]
-    extend(ODESystem(eqs, t, [], []; name = name), siso)
+@mtkmodel StaticNonLinearity begin
+    @parameters begin
+        func
+    end
+    @extend u, y = siso = SISO()
+    @equations begin
+        y ~ first(getdefault(func))(u)
+    end
 end
+StaticNonLinearity.f(func; name) = StaticNonLinearity.f(; name = name, func = [func])
 
 """
-    Abs(;name)
+    Abs(; name)
 
 Output the absolute value of the input.
 
@@ -221,7 +244,7 @@ See [`StaticNonLinearity`](@ref)
 @component Abs(; name) = StaticNonLinearity(abs; name)
 
 """
-    Sign(;name)
+    Sign(; name)
 
 Output the sign of the input
 
@@ -232,7 +255,7 @@ See [`StaticNonLinearity`](@ref)
 @component Sign(; name) = StaticNonLinearity(sign; name)
 
 """
-    Sqrt(;name)
+    Sqrt(; name)
 
 Output the square root of the input (input >= 0 required).
 
@@ -243,7 +266,7 @@ See [`StaticNonLinearity`](@ref)
 @component Sqrt(; name) = StaticNonLinearity(sqrt; name)
 
 """
-    Sin(;name)
+    Sin(; name)
 
 Output the sine of the input.
 
@@ -254,7 +277,7 @@ See [`StaticNonLinearity`](@ref)
 @component Sin(; name) = StaticNonLinearity(sin; name)
 
 """
-    Cos(;name)
+    Cos(; name)
 
 Output the cosine of the input.
 
@@ -265,7 +288,7 @@ See [`StaticNonLinearity`](@ref)
 @component Cos(; name) = StaticNonLinearity(cos; name)
 
 """
-    Tan(;name)
+    Tan(; name)
 
 Output the tangent of the input.
 
@@ -276,7 +299,7 @@ See [`StaticNonLinearity`](@ref)
 @component Tan(; name) = StaticNonLinearity(tan; name)
 
 """
-    Asin(;name)
+    Asin(; name)
 
 Output the arc sine of the input.
 
@@ -287,7 +310,7 @@ See [`StaticNonLinearity`](@ref)
 @component Asin(; name) = StaticNonLinearity(asin; name)
 
 """
-    Acos(;name)
+    Acos(; name)
 
 Output the arc cosine of the input.
 
@@ -298,7 +321,7 @@ See [`StaticNonLinearity`](@ref)
 @component Acos(; name) = StaticNonLinearity(acos; name)
 
 """
-    Atan(;name)
+    Atan(; name)
 
 Output the arc tangent of the input.
 
@@ -309,7 +332,7 @@ See [`StaticNonLinearity`](@ref)
 @component Atan(; name) = StaticNonLinearity(atan; name)
 
 """
-    Atan2(;name)
+    Atan2(; name)
 
 Output the arc tangent of the input.
 
@@ -319,18 +342,19 @@ Output the arc tangent of the input.
   - `input2`
   - `output`
 """
-@component function Atan2(; name)
-    @named input1 = RealInput()
-    @named input2 = RealInput()
-    @named output = RealOutput()
-    eqs = [
-        output.u ~ atan(input1.u, input2.u),
-    ]
-    compose(ODESystem(eqs, t, [], []; name = name), [input1, input2, output])
+@mtkmodel Atan2 begin
+    @components begin
+        input1 = RealInput()
+        input2 = RealInput()
+        output = RealOutput()
+    end
+    @equations begin
+        output.u ~ atan(input1.u, input2.u)
+    end
 end
 
 """
-    Sinh(;name)
+    Sinh(; name)
 
 Output the hyperbolic sine of the input.
 
@@ -341,7 +365,7 @@ See [`StaticNonLinearity`](@ref)
 @component Sinh(; name) = StaticNonLinearity(sinh; name)
 
 """
-    Cosh(;name)
+    Cosh(; name)
 
 Output the hyperbolic cosine of the input.
 
@@ -352,7 +376,7 @@ See [`StaticNonLinearity`](@ref)
 @component Cosh(; name) = StaticNonLinearity(cosh; name)
 
 """
-    Tanh(;name)
+    Tanh(; name)
 
 Output the hyperbolic tangent of the input.
 
@@ -363,7 +387,7 @@ See [`StaticNonLinearity`](@ref)
 @component Tanh(; name) = StaticNonLinearity(tanh; name)
 
 """
-    Exp(;name)
+    Exp(; name)
 
 Output the exponential (base e) of the input.
 
@@ -374,7 +398,7 @@ See [`StaticNonLinearity`](@ref)
 @component Exp(; name) = StaticNonLinearity(exp; name)
 
 """
-    Log(;name)
+    Log(; name)
 
 Output the natural (base e) logarithm of the input.
 
@@ -385,7 +409,7 @@ See [`StaticNonLinearity`](@ref)
 @component Log(; name) = StaticNonLinearity(log; name)
 
 """
-    Log10(;name)
+    Log10(; name)
 
 Output the base 10 logarithm of the input.
 
diff --git a/test/Blocks/math.jl b/test/Blocks/math.jl
index 4e1fe53f4..1ad2317fc 100644
--- a/test/Blocks/math.jl
+++ b/test/Blocks/math.jl
@@ -8,7 +8,7 @@ using OrdinaryDiffEq: ReturnCode.Success
 
 @testset "Gain" begin
     @named c = Constant(; k = 1)
-    @named gain = Gain(1;)
+    @named gain = Gain(; k = 1)
     @named int = Integrator(; k = 1)
     @named model = ODESystem([
             connect(c.output, gain.input),
@@ -27,7 +27,7 @@ end
 
 @testset "Feedback loop" begin
     @named c = Constant(; k = 2)
-    @named gain = Gain(1;)
+    @named gain = Gain(; k = 1)
     @named int = Integrator(; k = 1)
     @named fb = Feedback(;)
     @named model = ODESystem([
@@ -191,14 +191,14 @@ end
 
 @testset "MatrixGain" begin
     K = [1 2; 3 4]
-    @named gain = MatrixGain(K;)
+    @named gain = MatrixGain(; K)
     K = [1, 2]
-    @named gain = MatrixGain(K;)
+    @named gain = MatrixGain(; K)
     # TODO:
 end
 
 @testset "Sum" begin
-    @named s = Sum(2;)
+    @named s = Sum(; input.nin = 2)
     # TODO:
 end
 
diff --git a/test/Blocks/test_analysis_points.jl b/test/Blocks/test_analysis_points.jl
index fab92b37b..ccadd22ed 100644
--- a/test/Blocks/test_analysis_points.jl
+++ b/test/Blocks/test_analysis_points.jl
@@ -6,7 +6,7 @@ using ModelingToolkit: get_eqs, vars, @set!, get_iv
 using ControlSystemsBase
 
 @named P = FirstOrder(k = 1, T = 1)
-@named C = Gain(-1)
+@named C = Gain(; k = -1)
 t = ModelingToolkit.get_iv(P)
 
 @test_logs (:warn,) (:warn,) connect(P.input, :bad_connection, C.output)
@@ -106,7 +106,7 @@ matrices2, _ = linearize(sys, :plant_input, [P.output.u])
 ## Test with subsystems
 
 @named P = FirstOrder(k = 1, T = 1)
-@named C = Gain(1)
+@named C = Gain(; k = 1)
 @named add = Blocks.Add(k2 = -1)
 t = ModelingToolkit.get_iv(P)
 
@@ -303,7 +303,7 @@ G = CS.feedback(Pss, Kss, pos_feedback = true)
 
 ## Multiple analysis points ====================================================
 @named P = FirstOrder(k = 1, T = 1)
-@named C = Gain(1)
+@named C = Gain(; k = 1)
 @named add = Blocks.Add(k2 = -1)
 t = ModelingToolkit.get_iv(P)
 

From 2505ad332111900cf3787db93d6c08e6616cb9dc Mon Sep 17 00:00:00 2001
From: Venkateshprasad <32921645+ven-k@users.noreply.github.com>
Date: Mon, 3 Jul 2023 12:43:01 +0530
Subject: [PATCH 2/7] refactor: Blocks/continuous.jl

---
 src/Blocks/continuous.jl  | 183 ++++++++++++++++++++++----------------
 test/Blocks/continuous.jl |  14 +--
 2 files changed, 113 insertions(+), 84 deletions(-)

diff --git a/src/Blocks/continuous.jl b/src/Blocks/continuous.jl
index a2caab9ef..af34d36dd 100644
--- a/src/Blocks/continuous.jl
+++ b/src/Blocks/continuous.jl
@@ -1,7 +1,8 @@
 """
-    Integrator(;name, k=1, x_start=0.0)
+    Integrator(;name, k = 1, x = 0.0)
 
 Outputs `y = ∫k*u dt`, corresponding to the transfer function `1/s`.
+Initial value of integrator state `x` can be set with `x`
 
 # Connectors:
 
@@ -11,22 +12,25 @@ Outputs `y = ∫k*u dt`, corresponding to the transfer function `1/s`.
 # Parameters:
 
   - `k`: Gain of integrator
-  - `x_start`: Initial value of integrator
 """
-@component function Integrator(; name, k = 1, x_start = 0.0)
-    @named siso = SISO()
-    @unpack u, y = siso
-    sts = @variables x(t)=x_start [description = "State of Integrator $name"]
-    pars = @parameters k=k [description = "Gain of Integrator $name"]
-    eqs = [D(x) ~ k * u
-        y ~ x]
-    extend(ODESystem(eqs, t, sts, pars; name = name), siso)
+@mtkmodel Integrator begin
+    @extend u, y = siso = SISO()
+    @variables begin
+        x(t) = 0.0, [description = "State of Integrator"]
+    end
+    @parameters begin
+        k = 1, [description = "Gain of Integrator"]
+    end
+    @equations begin
+        D(x) ~ k * u
+        y ~ x
+    end
 end
-
 """
-    Derivative(; name, k=1, T, x_start=0.0)
+    Derivative(; name, k = 1, T, x = 0.0)
 
 Outputs an approximate derivative of the input. The transfer function of this block is
+Initial value of the state `x` can be set with `x`
 
 ```
 k       k
@@ -44,31 +48,37 @@ A smaller `T` leads to a more ideal approximation of the derivative.
 
   - `k`: Gain
   - `T`: [s] Time constants (T>0 required; T=0 is ideal derivative block)
-  - `x_start`: Initial value of state
 
 # Connectors:
 
   - `input`
   - `output`
 """
-@component function Derivative(; name, k = 1, T, x_start = 0.0)
-    @symcheck T > 0 || throw(ArgumentError("Time constant `T` has to be strictly positive"))
-    @named siso = SISO()
-    @unpack u, y = siso
-    sts = @variables x(t)=x_start [description = "State of Derivative $name"]
-    pars = @parameters T=T [description = "Time constant of Derivative $name"] k=k [
-        description = "Gain of Derivative $name",
-    ]
-    eqs = [D(x) ~ (u - x) / T
-        y ~ (k / T) * (u - x)]
-    extend(ODESystem(eqs, t, sts, pars; name = name), siso)
+@mtkmodel Derivative begin
+    @extend u, y = siso = SISO()
+    @variables begin
+        x(t) = 0.0, [description = "State of Derivative"]
+    end
+    @parameters begin
+        T = T, [description = "Time constant of Derivative"]
+        k = 1, [description = "Gain of Derivative"]
+    end
+    begin
+        @symcheck T > 0 ||
+                  throw(ArgumentError("Time constant `T` has to be strictly positive"))
+    end
+    @equations begin
+        D(x) ~ (u - x) / T
+        y ~ (k / T) * (u - x)
+    end
 end
 
 """
-    FirstOrder(; name, k=1, T, x_start=0.0, lowpass=true)
+    FirstOrder(; name, k = 1.0, T, x = 0.0, lowpass = true)
 
 A first-order filter with a single real pole in `s = -T` and gain `k`. If `lowpass=true` (default), the transfer function
 is given by `Y(s)/U(s) = `
+Initial value of the state `x` can be set with `x`
 
 ```
    k
@@ -88,7 +98,6 @@ sT + 1 - k
 
   - `k`: Gain
   - `T`: [s] Time constants (T>0 required)
-  - `x_start`: Initial value of state
 
 # Connectors:
 
@@ -97,21 +106,28 @@ sT + 1 - k
 
 See also [`SecondOrder`](@ref)
 """
-@component function FirstOrder(; name, k = 1, T, x_start = 0.0, lowpass = true)
-    @symcheck T > 0 || throw(ArgumentError("Time constant `T` has to be strictly positive"))
-    @named siso = SISO()
-    @unpack u, y = siso
-    sts = @variables x(t)=x_start [description = "State of FirstOrder filter $name"]
-    pars = @parameters T=T [description = "Time constant of FirstOrder filter $name"] k=k [
-        description = "Gain of FirstOrder $name",
-    ]
-    eqs = [D(x) ~ (k * u - x) / T
-        lowpass ? y ~ x : y ~ k * u - x]
-    extend(ODESystem(eqs, t, sts, pars; name = name), siso)
+@mtkmodel FirstOrder begin
+    @extend u, y = siso = SISO()
+    @variables begin
+        x(t) = 0.0, [description = "State of FirstOrder filter"]
+    end
+    @parameters begin
+        lowpass = true
+        T = T, [description = "Time constant of FirstOrder filter"]
+        k = 1.0, [description = "Gain of FirstOrder"]
+    end
+    begin
+        @symcheck T > 0 ||
+                  throw(ArgumentError("Time constant `T` has to be strictly positive"))
+    end
+    @equations begin
+        D(x) ~ (k * u - x) / T
+        getdefault(lowpass) ? y ~ x : y ~ k * u - x
+    end
 end
 
 """
-    SecondOrder(; name, k=1, w, d, x_start=0.0, xd_start=0.0)
+    SecondOrder(; name, k = 1.0, w, d, x = 0.0, xd = 0.0)
 
 A second-order filter with gain `k`, a bandwidth of `w` rad/s and relative damping `d`. The transfer function
 is given by `Y(s)/U(s) = `
@@ -124,44 +140,47 @@ s² + 2d*w*s + w^2
 
 Critical damping corresponds to `d=1`, which yields the fastest step response without overshoot, `d < 1` results in an underdamped filter while `d > 1` results in an overdamped filter.
 `d = 1/√2` corresponds to a Butterworth filter of order 2 (maximally flat frequency response).
+Initial value of the state `x` can be set with `x`, and of derivative state `xd` with `xd`.
 
 # Parameters:
 
   - `k`: Gain
   - `w`: [`rad/s`] Angular frequency
   - `d`: Damping
-  - `x_start`: Initial value of state (output)
-  - `xd_start`: Initial value of derivative of state (output)
 
 # Connectors:
 
   - `input`
   - `output`
 """
-@component function SecondOrder(; name, k = 1, w, d, x_start = 0.0, xd_start = 0.0)
-    @named siso = SISO()
-    @unpack u, y = siso
-    @variables x(t)=x_start [description = "State of SecondOrder filter $name"]
-    @variables xd(t)=xd_start [description = "Derivative state of SecondOrder filter $name"]
-    @parameters k=k [description = "Gain of SecondOrder $name"]
-    @parameters w=w [description = "Bandwidth of SecondOrder $name"]
-    @parameters d=d [description = "Relative damping of SecondOrder $name"]
-    eqs = [D(x) ~ xd
+@mtkmodel SecondOrder begin
+    @extend u, y = siso = SISO()
+    @variables begin
+        x(t) = 0.0, [description = "State of SecondOrder filter"]
+        xd(t) = 0.0, [description = "Derivative state of SecondOrder filter"]
+    end
+    @parameters begin
+        k = 1.0, [description = "Gain of SecondOrder"]
+        w, [description = "Bandwidth of SecondOrder"]
+        d, [description = "Relative damping of SecondOrder"]
+    end
+    @equations begin
+        D(x) ~ xd
         D(xd) ~ w * (w * (k * u - x) - 2 * d * xd)
-        y ~ x]
-    extend(ODESystem(eqs, t; name = name), siso)
+        y ~ x
+    end
 end
 
 """
-    PI(;name, k=1, T, x_start=0.0)
+    PI(;name, gainPI.k = 1.0, T, int.x = 0.0)
 
 Textbook version of a PI-controller without actuator saturation and anti-windup measure.
+Initial value of integrator state `x` can be set with `int.x`
+Initial value of gain  can be set with `gainPI.k`
 
 # Parameters:
 
-  - `k`: Gain
   - `T`: [s] Integrator time constant (T>0 required)
-  - `x_start`: Initial value for the integrator
 
 # Connectors:
 
@@ -170,22 +189,28 @@ Textbook version of a PI-controller without actuator saturation and anti-windup
 
 See also [`LimPI`](@ref)
 """
-@component function PI(; name, k = 1, T, x_start = 0.0)
-    @symcheck T > 0 || throw(ArgumentError("Time constant `T` has to be strictly positive"))
-    @named err_input = RealInput() # control error
-    @named ctr_output = RealOutput() # control signal
-    @named gainPI = Gain(k)
-    @named addPI = Add()
-    @named int = Integrator(k = 1 / T, x_start = x_start)
-    sys = [err_input, ctr_output, gainPI, addPI, int]
-    eqs = [
-        connect(err_input, addPI.input1),
-        connect(addPI.output, gainPI.input),
-        connect(gainPI.output, ctr_output),
-        connect(err_input, int.input),
-        connect(int.output, addPI.input2),
-    ]
-    ODESystem(eqs, t, [], []; name = name, systems = sys)
+@mtkmodel PI begin
+    @parameters begin
+        T, [description = "Integrator time constant"]
+    end
+    begin
+        @symcheck T > 0 ||
+                  throw(ArgumentError("Time constant `T` has to be strictly positive"))
+    end
+    @components begin
+        err_input = RealInput() # control error
+        ctr_output = RealOutput() # control signal
+        gainPI = Gain(; k = 1.0)
+        addPI = Add()
+        int = Integrator(k = 1 / T, x = 0.0)
+    end
+    @equations begin
+        connect(err_input, addPI.input1)
+        connect(addPI.output, gainPI.input)
+        connect(gainPI.output, ctr_output)
+        connect(err_input, int.input)
+        connect(int.output, addPI.input2)
+    end
 end
 
 """
@@ -224,12 +249,12 @@ See also [`LimPID`](@ref)
     @named gainPID = Gain(k)
     @named addPID = Add3()
     if with_I
-        @named int = Integrator(k = 1 / Ti, x_start = xi_start)
+        @named int = Integrator(k = 1 / Ti, x = xi_start)
     else
         @named Izero = Constant(k = 0)
     end
     if with_D
-        @named der = Derivative(k = Td, T = 1 / Nd, x_start = xd_start)
+        @named der = Derivative(k = Td, T = 1 / Nd, x = xd_start)
     else
         @named Dzero = Constant(k = 0)
     end
@@ -265,16 +290,16 @@ See also [`LimPID`](@ref)
 end
 
 """
-    LimPI(;name, k=1, T, u_max=1, u_min=-u_max, Ta)
+    LimPI(; name, T, Ta, k = 1.0, x_start = 0.0, u_max = 1.0, u_min = -u_max)
 
 Text-book version of a PI-controller with actuator saturation and anti-windup measure.
+Initial value of gain  can be set with `gainPI.k`
+Initial value of integrator state `x` can be set with `int.x`
 
 # Parameters:
 
-  - `k`: Gain
   - `T`: [s] Integrator time constant (T>0 required)
   - `Ta`: [s] Tracking time constant (Ta>0 required)
-  - `x_start`: Initial value for the integrator
 
 # Connectors:
 
@@ -291,7 +316,7 @@ Text-book version of a PI-controller with actuator saturation and anti-windup me
     @named gainPI = Gain(k)
     @named addPI = Add()
     @named addTrack = Add()
-    @named int = Integrator(k = 1 / T, x_start = x_start)
+    @named int = Integrator(k = 1 / T, x = x_start)
     @named limiter = Limiter(y_max = u_max, y_min = u_min)
     @named addSat = Add(k1 = 1, k2 = -1)
     @named gainTrack = Gain(1 / Ta)
@@ -376,7 +401,7 @@ where the transfer function for the derivative includes additional filtering, se
     @named measurement = RealInput()
     @named ctr_output = RealOutput() # control signal
     @named addP = Add(k1 = wp, k2 = -1)
-    @named gainPID = Gain(k)
+    @named gainPID = Gain(; k)
     @named addPID = Add3()
     @named limiter = Limiter(y_max = u_max, y_min = u_min)
     if with_I
@@ -387,12 +412,12 @@ where the transfer function for the derivative includes additional filtering, se
         else
             @named addI = Add(k1 = 1, k2 = -1)
         end
-        @named int = Integrator(k = 1 / Ti, x_start = xi_start)
+        @named int = Integrator(k = 1 / Ti, x = xi_start)
     else
         @named Izero = Constant(k = 0)
     end
     if with_D
-        @named der = Derivative(k = Td, T = 1 / Nd, x_start = xd_start)
+        @named der = Derivative(k = Td, T = 1 / Nd, x = xd_start)
         @named addD = Add(k1 = wd, k2 = -1)
     else
         @named Dzero = Constant(k = 0)
diff --git a/test/Blocks/continuous.jl b/test/Blocks/continuous.jl
index 5a1f09746..3dffa3b1f 100644
--- a/test/Blocks/continuous.jl
+++ b/test/Blocks/continuous.jl
@@ -13,10 +13,10 @@ an integrator with a constant input is often used together with the system under
 
 @testset "Constant" begin
     @named c = Constant(; k = 1)
-    @named int = Integrator()
+    @named int = Integrator(x = 1)
     @named iosys = ODESystem(connect(c.output, int.input), t, systems = [int, c])
     sys = structural_simplify(iosys)
-    prob = ODEProblem(sys, Pair[int.x => 1.0], (0.0, 1.0))
+    prob = ODEProblem(sys, Pair[], (0.0, 1.0))
     sol = solve(prob, Rodas4())
     @test sol.retcode == Success
     @test all(sol[c.output.u] .≈ 1)
@@ -147,7 +147,7 @@ end
 @testset "PI" begin
     re_val = 2
     @named ref = Constant(; k = re_val)
-    @named pi_controller = PI(k = 1, T = 1)
+    @named pi_controller = PI(int.k = 1, T = 1)
     @named plant = Plant()
     @named fb = Feedback()
     @named model = ODESystem([
@@ -227,8 +227,12 @@ end
 @testset "LimPI" begin
     re_val = 1
     @named ref = Constant(; k = re_val)
-    @named pi_controller_lim = LimPI(k = 3, T = 0.5, u_max = 1.5, u_min = -1.5, Ta = 0.1)
-    @named pi_controller = PI(k = 3, T = 0.5)
+    @named pi_controller_lim = LimPI(k = 3,
+        T = 0.5,
+        u_max = 1.5,
+        u_min = -1.5,
+        Ta = 0.1)
+    @named pi_controller = PI(gainPI.k = 3, T = 0.5)
     @named sat = Limiter(y_max = 1.5, y_min = -1.5)
     @named plant = Plant()
     @named fb = Feedback()

From 9875e7fced494995ef8f68ce01e2f70ce75fb8b3 Mon Sep 17 00:00:00 2001
From: Venkateshprasad <32921645+ven-k@users.noreply.github.com>
Date: Mon, 3 Jul 2023 12:46:14 +0530
Subject: [PATCH 3/7] refactor: Blocks/nonlinear.jl

---
 src/Blocks/nonlinear.jl | 67 +++++++++++++++++++++++------------------
 1 file changed, 37 insertions(+), 30 deletions(-)

diff --git a/src/Blocks/nonlinear.jl b/src/Blocks/nonlinear.jl
index 502b50478..bab526a83 100644
--- a/src/Blocks/nonlinear.jl
+++ b/src/Blocks/nonlinear.jl
@@ -2,7 +2,7 @@ _clamp(u, u_min, u_max) = max(min(u, u_max), u_min)
 _dead_zone(u, u_min, u_max) = ifelse(u > u_max, u - u_max, ifelse(u < u_min, u - u_min, 0))
 
 """
-    Limiter(;name, y_max, y_min=y_max > 0 ? -y_max : -Inf)
+    Limiter(;name, y_max, y_min = y_max > 0 ? -y_max : -Inf)
 
 Limit the range of a signal.
 
@@ -30,7 +30,7 @@ Limit the range of a signal.
 end
 
 """
-    DeadZone(; name, u_max, u_min=-u_max)
+    DeadZone(; name, u_max, u_min = -u_max)
 
 The DeadZone block defines a region of zero output.
 If the input is within `u_min` ... `u_max`, the output is zero. Outside of this zone, the output is a linear function of the input with a slope of 1.
@@ -56,50 +56,57 @@ If the input is within `u_min` ... `u_max`, the output is zero. Outside of this
   - `input`
   - `output`
 """
-@component function DeadZone(; name, u_max, u_min = -u_max)
-    if !ModelingToolkit.isvariable(u_max)
-        u_max ≥ u_min || throw(ArgumentError("`u_min` must be smaller than `u_max`"))
+@mtkmodel DeadZone begin
+    @parameters begin
+        u_max, [description = "Upper limit of dead zone of DeadZone"]
+        u_min = -u_max, [description = "Lower limit of dead zone of DeadZone"]
+    end
+    begin
+        if !ModelingToolkit.isvariable(u_max)
+            u_max ≥ u_min || throw(ArgumentError("`u_min` must be smaller than `u_max`"))
+        end
+    end
+
+    @extend u, y = siso = SISO()
+
+    @equations begin
+        y ~ _dead_zone(u, u_min, u_max)
     end
-    @named siso = SISO()
-    @unpack u, y = siso
-    pars = @parameters u_max=u_max [
-        description = "Upper limit of dead zone of DeadZone $name",
-    ] u_min=u_min [description = "Lower limit of dead zone of DeadZone $name"]
-    eqs = [
-        y ~ _dead_zone(u, u_min, u_max),
-    ]
-    extend(ODESystem(eqs, t, [], pars; name = name), siso)
 end
 
 """
-    SlewRateLimiter(;name, rising=1, falling=-rising, Td=0.001, y_start=0.0)
+    SlewRateLimiter(; name, y_start, rising = 1.0, falling = -rising, Td = 0.001)
 
 Limits the slew rate of a signal.
+Initial value of state `Y` can be set with `int.y`
 
 # Parameters:
 
   - `rising`: Maximum rising slew rate
   - `falling`: Maximum falling slew rate
   - `Td`: [s] Derivative time constant
+  - `y_start`: Initial value of `y` state of SISO
 
 # Connectors:
 
   - `input`
   - `output`
 """
-@component function SlewRateLimiter(; name, rising = 1, falling = -rising, Td = 0.001,
-    y_start = 0.0)
-    rising ≥ falling || throw(ArgumentError("`rising` must be smaller than `falling`"))
-    Td > 0 || throw(ArgumentError("Time constant `Td` must be strictly positive"))
-    @named siso = SISO(y_start = y_start)
-    @unpack u, y = siso
-    pars = @parameters rising=rising [
-        description = "Maximum rising slew rate of SlewRateLimiter $name",
-    ] falling=falling [description = "Maximum falling slew rate of SlewRateLimiter $name"] Td=Td [
-        description = "Derivative time constant of SlewRateLimiter $name",
-    ]
-    eqs = [
-        D(y) ~ max(min((u - y) / Td, rising), falling),
-    ]
-    extend(ODESystem(eqs, t, [], pars; name = name), siso)
+@mtkmodel SlewRateLimiter begin
+    @parameters begin
+        rising = 1.0, [description = "Maximum rising slew rate of SlewRateLimiter"]
+        falling = -rising, [description = "Derivative time constant of SlewRateLimiter"]
+        Td = 0.001, [description = "Derivative time constant"]
+        y_start
+    end
+    begin
+        getdefault(rising) ≥ getdefault(falling) ||
+            throw(ArgumentError("`rising` must be smaller than `falling`"))
+        getdefault(Td) > 0 ||
+            throw(ArgumentError("Time constant `Td` must be strictly positive"))
+    end
+    @extend u, y = siso = SISO(y_start = y_start)
+    @equations begin
+        D(y) ~ max(min((u - y) / Td, rising), falling)
+    end
 end

From 0d4a2dc64a9b48ce6fe5c8174d7eb3e58aa571e8 Mon Sep 17 00:00:00 2001
From: Venkateshprasad <32921645+ven-k@users.noreply.github.com>
Date: Mon, 3 Jul 2023 12:48:22 +0530
Subject: [PATCH 4/7] refactor: Blocks/sources.jl (limited)

---
 src/Blocks/sources.jl                     | 61 ++++++++++++++++-------
 src/Electrical/Analog/ideal_components.jl | 38 ++++++++------
 test/Blocks/sources.jl                    |  2 +-
 test/demo.jl                              |  2 +-
 4 files changed, 68 insertions(+), 35 deletions(-)

diff --git a/src/Blocks/sources.jl b/src/Blocks/sources.jl
index 1b640de9c..a0c753cc7 100644
--- a/src/Blocks/sources.jl
+++ b/src/Blocks/sources.jl
@@ -59,6 +59,8 @@ function triangular(x, f, amplitude, offset, start_time)
 end
 
 """
+    Constant(; name, k = 0.0)
+
 Generate constant signal.
 
 # Parameters:
@@ -69,17 +71,20 @@ Generate constant signal.
 
   - `output`
 """
-@component function Constant(; name, k = 1)
-    @named output = RealOutput()
-    pars = @parameters k=k [description = "Constant output value of block $name"]
-    eqs = [
-        output.u ~ k,
-    ]
-    compose(ODESystem(eqs, t, [], pars; name = name), [output])
+@mtkmodel Constant begin
+    @components begin
+        output = RealOutput()
+    end
+    @parameters begin
+        k = 0.0, [description = "Constant output value of block"]
+    end
+    @equations begin
+        output.u ~ k
+    end
 end
 
 """
-    TimeVaryingFunction(f; t=t, name)
+    TimeVaryingFunction(f; name)
 
 Outputs ``f(t)``.
 
@@ -88,15 +93,23 @@ The input variable `t` can be changed by passing a different variable as the key
 # Connectors:
 - `output`
 """
-@component function TimeVaryingFunction(f; t = t, name)
-    @named output = RealOutput()
-    eqs = [
-        output.u ~ f(t),
-    ]
-    compose(ODESystem(eqs, Blocks.t; name = name), [output])
+@mtkmodel TimeVaryingFunction begin
+    @parameters begin
+        f
+    end
+    @components begin
+        output = RealOutput()
+    end
+    @equations begin
+        output.u ~ first(getdefault(f))(t)
+    end
 end
+TimeVaryingFunction.f(f; name) = TimeVaryingFunction.f(; f = [f], name)
 
 """
+    Sine(; name, frequency, amplitude = 1, phase = 0, offset = 0, start_time = 0,
+    smooth = false)
+
 Generate sine signal.
 
 # Parameters:
@@ -138,7 +151,10 @@ Generate sine signal.
 end
 
 """
-Generate cosine signal.
+    Cosine(; name, frequency, amplitude = 1, phase = 0, offset = 0, start_time = 0,
+    smooth = false)
+
+Cosine signal.
 
 # Parameters:
 - `frequency`: [Hz] Frequency of sine wave
@@ -177,6 +193,8 @@ Generate cosine signal.
 end
 
 """
+    ContinuousClock(; name, offset = 0, start_time = 0)
+
 Generate current time signal.
 
 # Parameters:
@@ -199,6 +217,8 @@ Generate current time signal.
 end
 
 """
+Ramp(; name, height = 1, duration = 1, offset = 0, start_time = 0, smooth = false)
+
 Generate ramp signal.
 
 # Parameters:
@@ -239,6 +259,8 @@ Generate ramp signal.
 end
 
 """
+    Square(; name, frequency = 1.0, amplitude = 1.0, offset = 0.0, start_time = 0.0,
+    smooth = false)
 Generate smooth square signal.
 
 # Parameters:
@@ -321,7 +343,9 @@ Generate step signal.
 end
 
 """
-Generate exponentially damped sine signal.
+    ExpSine(; name, frequency, amplitude = 1, damping = 0.1, phase = 0, offset = 0, start_time = 0, smooth = false)
+
+Exponentially damped sine signal.
 
 # Parameters:
 
@@ -367,6 +391,9 @@ Generate exponentially damped sine signal.
 end
 
 """
+    Triangular(; name, amplitude = 1.0, frequency = 1.0, offset = 0.0,
+    start_time = 0.0, smooth = false)
+
 Generate smooth triangular signal for frequencies less than or equal to 25 Hz
 
 # Parameters:
@@ -548,7 +575,7 @@ end
 """
     SampledData(; name, buffer)
 
-data input component.  
+data input component.
 
 # Parameters:
   - `buffer`: a `Parameter` type which holds the data and sample time
diff --git a/src/Electrical/Analog/ideal_components.jl b/src/Electrical/Analog/ideal_components.jl
index ed0b9a808..75104ac79 100644
--- a/src/Electrical/Analog/ideal_components.jl
+++ b/src/Electrical/Analog/ideal_components.jl
@@ -89,14 +89,17 @@ Creates an ideal capacitor.
   - `C`: [`F`] Capacitance
   - `v_start`: [`V`] Initial voltage of capacitor
 """
-@component function Capacitor(; name, C, v_start = 0.0)
-    @named oneport = OnePort(; v_start = v_start)
-    @unpack v, i = oneport
-    pars = @parameters C = C
-    eqs = [
-        D(v) ~ i / C,
-    ]
-    extend(ODESystem(eqs, t, [], pars; name = name), oneport)
+@mtkmodel Capacitor begin
+    @parameters begin
+        C
+    end
+    @variables begin
+        v
+    end
+    @extend v, i = oneport = OnePort(; v = v)
+    @equations begin
+        D(v) ~ i / C
+    end
 end
 
 """
@@ -118,14 +121,17 @@ See [OnePort](@ref)
   - `L`: [`H`] Inductance
   - `i_start`: [`A`] Initial current through inductor
 """
-@component function Inductor(; name, L, i_start = 0.0)
-    @named oneport = OnePort(; i_start = i_start)
-    @unpack v, i = oneport
-    pars = @parameters L = L
-    eqs = [
-        D(i) ~ 1 / L * v,
-    ]
-    extend(ODESystem(eqs, t, [], pars; name = name), oneport)
+@mtkmodel Inductor begin # name, L, i_start = 0.0)
+    @parameters begin
+        L
+    end
+    @variables begin
+        i
+    end
+    @extend v, i = oneport = OnePort(; i = i)
+    @equations begin
+        D(i) ~ 1 / L * v
+    end
 end
 
 """
diff --git a/test/Blocks/sources.jl b/test/Blocks/sources.jl
index 2ad5160eb..f0ef3c952 100644
--- a/test/Blocks/sources.jl
+++ b/test/Blocks/sources.jl
@@ -37,7 +37,7 @@ end
         systems = [int, src])
     sys = structural_simplify(iosys)
 
-    prob = ODEProblem(sys, Pair[int.x => 0.0], (0.0, 10.0))
+    prob = ODEProblem(sys, Pair[], (0.0, 10.0))
 
     sol = solve(prob, Rodas4())
     @test sol.retcode == Success
diff --git a/test/demo.jl b/test/demo.jl
index 9f47185c9..3ce518687 100644
--- a/test/demo.jl
+++ b/test/demo.jl
@@ -12,7 +12,7 @@ using Test
     @named capacitor = Capacitor(C = C)
     @named voltage = Voltage()
     @named ground = Ground()
-    @named source = Constant()
+    @named source = Constant(k = 1)
 
     rc_eqs = [connect(source.output, voltage.V)
         connect(voltage.p, resistor.p)

From 4acbee659d09e9ed50e42ea592e3ec6b6c8ac1b4 Mon Sep 17 00:00:00 2001
From: Venkateshprasad <32921645+ven-k@users.noreply.github.com>
Date: Mon, 3 Jul 2023 12:48:46 +0530
Subject: [PATCH 5/7] refactor: Blocks/utils.jl (limited)

---
 src/Blocks/Blocks.jl                      |  1 +
 src/Blocks/utils.jl                       | 33 +++++++++++++-------
 src/Electrical/Analog/ideal_components.jl | 38 ++++++++++-------------
 test/Hydraulic/isothermal_compressible.jl |  2 +-
 4 files changed, 39 insertions(+), 35 deletions(-)

diff --git a/src/Blocks/Blocks.jl b/src/Blocks/Blocks.jl
index 38331019b..1a7cdb5c6 100644
--- a/src/Blocks/Blocks.jl
+++ b/src/Blocks/Blocks.jl
@@ -5,6 +5,7 @@ module Blocks
 using ModelingToolkit, Symbolics
 using IfElse: ifelse
 import ..@symcheck
+using ModelingToolkit: getdefault
 
 @parameters t
 D = Differential(t)
diff --git a/src/Blocks/utils.jl b/src/Blocks/utils.jl
index b9ff73c7a..59db3655b 100644
--- a/src/Blocks/utils.jl
+++ b/src/Blocks/utils.jl
@@ -55,27 +55,36 @@ Connector with one output signal of type Real.
 """ RealOutput
 
 """
-    SISO(;name, u_start=0.0, y_start=0.0)
+    SISO(;name, u_start = 0.0, y_start = 0.0)
 
 Single input single output (SISO) continuous system block.
 
 # Parameters:
 
-  - `u_start`: Initial value for the input
-  - `y_start`: Initial value for the output
+  - `u`: Initial value for the input
+  - `y`: Initial value for the output
 """
-@component function SISO(; name, u_start = 0.0, y_start = 0.0)
-    @named input = RealInput(u_start = u_start)
-    @named output = RealOutput(u_start = y_start)
-    @variables(u(t)=u_start, [description = "Input of SISO system $name"],
-        y(t)=y_start, [description = "Output of SISO system $name"],)
-    eqs = [u ~ input.u
-        y ~ output.u]
-    return ODESystem(eqs, t, [u, y], []; name = name, systems = [input, output])
+@mtkmodel SISO begin
+    @parameters begin
+        u_start = 0.0
+        y_start = 0.0
+    end
+    @variables begin
+        u(t) = u_start, [description = "Input of SISO system"]
+        y(t) = y_start, [description = "Output of SISO system"]
+    end
+    @components begin
+        input = RealInput(u_start = 0.0)
+        output = RealOutput(u_start = 0.0)
+    end
+    @equations begin
+        u ~ input.u
+        y ~ output.u
+    end
 end
 
 """
-    MIMO(;name, nin=1, nout=1, u_start=zeros(nin), y_start=zeros(nout))
+    MIMO(; name, nin = 1, nout = 1, u_start = zeros(nin), y_start = zeros(nout))
 
 Base class for a multiple input multiple output (MIMO) continuous system block.
 
diff --git a/src/Electrical/Analog/ideal_components.jl b/src/Electrical/Analog/ideal_components.jl
index 75104ac79..ed0b9a808 100644
--- a/src/Electrical/Analog/ideal_components.jl
+++ b/src/Electrical/Analog/ideal_components.jl
@@ -89,17 +89,14 @@ Creates an ideal capacitor.
   - `C`: [`F`] Capacitance
   - `v_start`: [`V`] Initial voltage of capacitor
 """
-@mtkmodel Capacitor begin
-    @parameters begin
-        C
-    end
-    @variables begin
-        v
-    end
-    @extend v, i = oneport = OnePort(; v = v)
-    @equations begin
-        D(v) ~ i / C
-    end
+@component function Capacitor(; name, C, v_start = 0.0)
+    @named oneport = OnePort(; v_start = v_start)
+    @unpack v, i = oneport
+    pars = @parameters C = C
+    eqs = [
+        D(v) ~ i / C,
+    ]
+    extend(ODESystem(eqs, t, [], pars; name = name), oneport)
 end
 
 """
@@ -121,17 +118,14 @@ See [OnePort](@ref)
   - `L`: [`H`] Inductance
   - `i_start`: [`A`] Initial current through inductor
 """
-@mtkmodel Inductor begin # name, L, i_start = 0.0)
-    @parameters begin
-        L
-    end
-    @variables begin
-        i
-    end
-    @extend v, i = oneport = OnePort(; i = i)
-    @equations begin
-        D(i) ~ 1 / L * v
-    end
+@component function Inductor(; name, L, i_start = 0.0)
+    @named oneport = OnePort(; i_start = i_start)
+    @unpack v, i = oneport
+    pars = @parameters L = L
+    eqs = [
+        D(i) ~ 1 / L * v,
+    ]
+    extend(ODESystem(eqs, t, [], pars; name = name), oneport)
 end
 
 """
diff --git a/test/Hydraulic/isothermal_compressible.jl b/test/Hydraulic/isothermal_compressible.jl
index 7d831ac02..3d637fdf8 100644
--- a/test/Hydraulic/isothermal_compressible.jl
+++ b/test/Hydraulic/isothermal_compressible.jl
@@ -256,7 +256,7 @@ end
         if use_input
             @named input = B.SampledData(Float64)
         else
-            @named input = B.TimeVaryingFunction(f; t)
+            @named input = B.TimeVaryingFunction(f)
         end
 
         push!(systems, input)

From 518df2b72f9f964468039e3ad316076e0c32f8d1 Mon Sep 17 00:00:00 2001
From: Venkateshprasad <32921645+ven-k@users.noreply.github.com>
Date: Tue, 11 Jul 2023 19:23:20 +0530
Subject: [PATCH 6/7] docs: set MTK to 8

---
 docs/Project.toml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/Project.toml b/docs/Project.toml
index 9027ab4aa..d69549620 100644
--- a/docs/Project.toml
+++ b/docs/Project.toml
@@ -13,7 +13,7 @@ ControlSystemsBase = "1.1"
 DifferentialEquations = "7.6"
 Documenter = "0.27"
 IfElse = "0.1"
-ModelingToolkit = "8.33"
+ModelingToolkit = "8"
 ModelingToolkitStandardLibrary = "1.8"
 OrdinaryDiffEq = "6.31"
 Plots = "1.36"
\ No newline at end of file

From 6a09473f58635468b526169e02b47fa69ce918fc Mon Sep 17 00:00:00 2001
From: Venkateshprasad <32921645+ven-k@users.noreply.github.com>
Date: Mon, 17 Jul 2023 11:39:44 +0530
Subject: [PATCH 7/7] refactor: update the arglist of non-dsl components to
 match the style of dsl components

- this will allow upgradation of those without breaking again
---
 src/Blocks/continuous.jl  | 36 +++++++++++++++++-------------------
 test/Blocks/continuous.jl |  8 ++++----
 2 files changed, 21 insertions(+), 23 deletions(-)

diff --git a/src/Blocks/continuous.jl b/src/Blocks/continuous.jl
index af34d36dd..4cacd52df 100644
--- a/src/Blocks/continuous.jl
+++ b/src/Blocks/continuous.jl
@@ -214,7 +214,7 @@ See also [`LimPI`](@ref)
 end
 
 """
-    PID(;name, k=1, Ti=false, Td=false, Nd=10, xi_start=0, xd_start=0)
+    PID(;name, k=1, Ti=false, Td=false, Nd=10, int__x=0, der__x=0)
 
 Text-book version of a PID-controller without actuator saturation and anti-windup measure.
 
@@ -224,8 +224,8 @@ Text-book version of a PID-controller without actuator saturation and anti-windu
   - `Ti`: [s] Integrator time constant (Ti>0 required). If set to false, no integral action is used.
   - `Td`: [s] Derivative time constant (Td>0 required). If set to false, no derivative action is used.
   - `Nd`: [s] Time constant for the derivative approximation (Nd>0 required; Nd=0 is ideal derivative).
-  - `x_start`: Initial value for the integrator.
-  - `xd_start`: Initial value for the derivative state.
+  - `int__x`: Initial value for the integrator.
+  - `der__x`: Initial value for the derivative state.
 
 # Connectors:
 
@@ -234,8 +234,8 @@ Text-book version of a PID-controller without actuator saturation and anti-windu
 
 See also [`LimPID`](@ref)
 """
-@component function PID(; name, k = 1, Ti = false, Td = false, Nd = 10, xi_start = 0,
-    xd_start = 0)
+@component function PID(; name, k = 1, Ti = false, Td = false, Nd = 10, int__x = 0,
+    der__x = 0)
     with_I = !isequal(Ti, false)
     with_D = !isequal(Td, false)
     @named err_input = RealInput() # control error
@@ -249,12 +249,12 @@ See also [`LimPID`](@ref)
     @named gainPID = Gain(k)
     @named addPID = Add3()
     if with_I
-        @named int = Integrator(k = 1 / Ti, x = xi_start)
+        @named int = Integrator(k = 1 / Ti, x = int__x)
     else
         @named Izero = Constant(k = 0)
     end
     if with_D
-        @named der = Derivative(k = Td, T = 1 / Nd, x = xd_start)
+        @named der = Derivative(k = Td, T = 1 / Nd, x = der__x)
     else
         @named Dzero = Constant(k = 0)
     end
@@ -290,11 +290,9 @@ See also [`LimPID`](@ref)
 end
 
 """
-    LimPI(; name, T, Ta, k = 1.0, x_start = 0.0, u_max = 1.0, u_min = -u_max)
+    LimPI(; name, T, Ta, k = 1.0, int__x = 0.0, u_max = 1.0, u_min = -u_max)
 
 Text-book version of a PI-controller with actuator saturation and anti-windup measure.
-Initial value of gain  can be set with `gainPI.k`
-Initial value of integrator state `x` can be set with `int.x`
 
 # Parameters:
 
@@ -306,7 +304,7 @@ Initial value of integrator state `x` can be set with `int.x`
   - `err_input`
   - `ctr_output`
 """
-@component function LimPI(; name, k = 1, T, u_max, u_min = -u_max, Ta, x_start = 0.0)
+@component function LimPI(; name, k = 1, T, u_max, u_min = -u_max, Ta, int__x = 0.0)
     @symcheck Ta > 0 ||
               throw(ArgumentError("Time constant `Ta` has to be strictly positive"))
     @symcheck T > 0 || throw(ArgumentError("Time constant `T` has to be strictly positive"))
@@ -316,7 +314,7 @@ Initial value of integrator state `x` can be set with `int.x`
     @named gainPI = Gain(k)
     @named addPI = Add()
     @named addTrack = Add()
-    @named int = Integrator(k = 1 / T, x = x_start)
+    @named int = Integrator(k = 1 / T, x = int__x)
     @named limiter = Limiter(y_max = u_max, y_min = u_min)
     @named addSat = Add(k1 = 1, k2 = -1)
     @named gainTrack = Gain(1 / Ta)
@@ -376,8 +374,8 @@ where the transfer function for the derivative includes additional filtering, se
     u_max = Inf,
     u_min = u_max > 0 ? -u_max : -Inf,
     gains = false,
-    xi_start = 0.0,
-    xd_start = 0.0)
+    int__x = 0.0,
+    der__x = 0.0)
     with_I = !isequal(Ti, false)
     with_D = !isequal(Td, false)
     with_AWM = Ni != Inf
@@ -412,12 +410,12 @@ where the transfer function for the derivative includes additional filtering, se
         else
             @named addI = Add(k1 = 1, k2 = -1)
         end
-        @named int = Integrator(k = 1 / Ti, x = xi_start)
+        @named int = Integrator(k = 1 / Ti, x = int__x)
     else
         @named Izero = Constant(k = 0)
     end
     if with_D
-        @named der = Derivative(k = Td, T = 1 / Nd, x = xd_start)
+        @named der = Derivative(k = Td, T = 1 / Nd, x = der__x)
         @named addD = Add(k1 = wd, k2 = -1)
     else
         @named Dzero = Constant(k = 0)
@@ -473,7 +471,7 @@ where the transfer function for the derivative includes additional filtering, se
 end
 
 """
-    StateSpace(A, B, C, D=0; x_start=zeros(size(A,1)), u0=zeros(size(B,2)), y0=zeros(size(C,1)), name)
+    StateSpace(A, B, C, D = 0; x =    zeros(size(A,1)), u0 = zeros(size(B,2)), y0 = zeros(size(C,1)), name)
 
 A linear, time-invariant state-space system on the form.
 
@@ -506,7 +504,7 @@ y &= h(x, u)
 
 linearized around the operating point `x₀, u₀`, we have `y0, u0 = h(x₀, u₀), u₀`.
 """
-@component function StateSpace(; A, B, C, D = nothing, x_start = zeros(size(A, 1)), name,
+@component function StateSpace(; A, B, C, D = nothing, x = zeros(size(A, 1)), name,
     u0 = zeros(size(B, 2)), y0 = zeros(size(C, 1)))
     nx, nu, ny = size(A, 1), size(B, 2), size(C, 1)
     size(A, 2) == nx || error("`A` has to be a square matrix.")
@@ -522,7 +520,7 @@ linearized around the operating point `x₀, u₀`, we have `y0, u0 = h(x₀, u
     end
     @named input = RealInput(nin = nu)
     @named output = RealOutput(nout = ny)
-    @variables x(t)[1:nx]=x_start [
+    @variables x(t)[1:nx]=x [
         description = "State variables of StateSpace system $name",
     ]
     # pars = @parameters A=A B=B C=C D=D # This is buggy
diff --git a/test/Blocks/continuous.jl b/test/Blocks/continuous.jl
index 3dffa3b1f..bdd4739c8 100644
--- a/test/Blocks/continuous.jl
+++ b/test/Blocks/continuous.jl
@@ -92,7 +92,7 @@ end
     B = [0, 1]
     C = [0.9 1;]
     D = [0;;]
-    @named ss = StateSpace(; A, B, C, D, x_start = zeros(2))
+    @named ss = StateSpace(; A, B, C, D, x = zeros(2))
     @named c = Constant(; k = 1)
     @named model = ODESystem([
             connect(c.output, ss.input),
@@ -113,7 +113,7 @@ end
     # non-zero operating point
     u0 = [1] # This causes no effective input to the system since c.k = 1
     y0 = [2]
-    @named ss = StateSpace(; A, B, C, D, x_start = zeros(2), u0, y0)
+    @named ss = StateSpace(; A, B, C, D, x = zeros(2), u0, y0)
     @named model = ODESystem([
             connect(c.output, ss.input),
         ],
@@ -133,11 +133,11 @@ end
 """
 Second order demo plant
 """
-@component function Plant(; name, x_start = zeros(2))
+@component function Plant(; name, x = zeros(2))
     @named input = RealInput()
     @named output = RealOutput()
     D = Differential(t)
-    sts = @variables x1(t)=x_start[1] x2(t)=x_start[2]
+    sts = @variables x1(t)=x[1] x2(t)=x[2]
     eqs = [D(x1) ~ x2
         D(x2) ~ -x1 - 0.5 * x2 + input.u
         output.u ~ 0.9 * x1 + x2]