Fix non-commutative multiplication of named systems

src/glover_mcfarlane.jl

@@ -68,12 +68,11 @@ Skogestad gives the following general advice:
     of methods available including normalization with respect to the magnitude of
     the maximum or average value of the signal in question. If one is to go straight to a design the following variation has
     proved useful in practice:
-    (a) The outputs are scaled such that equal magnitudes of cross-coupling into each
+    - The outputs are scaled such that equal magnitudes of cross-coupling into each
         of the outputs is equally undesirable.
-    (b) Each input is scaled by a given percentage (say 10%) of its expected range
+    - Each input is scaled by a given percentage (say 10%) of its expected range
         of operation. That is, the inputs are scaled to reflect the relative actuator
-        capabilities. An example of this type of scaling is given in the aero-engine
-        case study of Chapter 12.
+        capabilities.
 2. Order the inputs and outputs so that the plant is as diagonal as possible. The
     relative gain array [`rga`](@ref) can be useful here. The purpose of this pseudo-diagonalization
     is to ease the design of the pre- and post-compensators which, for simplicity, will

src/named_systems2.jl

@@ -252,8 +252,17 @@ function Base.:*(s1::Number, s2::NamedStateSpace{T, S}) where {T <: CS.TimeEvolu
     )
 end
 
+function Base.:*(s1::NamedStateSpace{T, S}, s2::Number) where {T <: CS.TimeEvolution, S}
+    return NamedStateSpace{T,S}(
+        s1.sys*s2,
+        s1.x,
+        [Symbol(string(u)*"_scaled") for u in s1.u],
+        s1.y,
+    )
+end
+
 function Base.:/(s::NamedStateSpace{T, S}, n::Number) where {T <: CS.TimeEvolution, S}
-    (1/n)*s
+    s*(1/n)
 end
 ##
 
@@ -354,6 +363,8 @@ Addition and subtraction nodes are achieved by creating a linear combination nod
 - `z1`: outputs (can overlap with `y1`)
 - `verbose`: Issue warnings for signals that have no connection
 
+Note: Positive feedback is used, controllers that are intended to be connected with negative feedback must thus be negated.
+
 Example:
 The following complicated feedback interconnection
 
@@ -404,9 +415,9 @@ function connect(systems; u1::Vector{Symbol}, y1::Vector{Symbol}, w1::Vector{Sym
 
     if verbose
         leftover_inputs = setdiff(full.u, [u1; w1])
-        isempty(leftover_inputs) || @warn("The following inputs were unconnected $leftover_inputs")
+        isempty(leftover_inputs) || @warn("The following inputs were unconnected $leftover_inputs, ignore this warning if you rely on prefix matching")
         leftover_outputs = setdiff(full.y, z1 == (:) ? y1 : [y1; z1])
-        isempty(leftover_outputs) || @warn("The following outputs were unconnected $leftover_outputs")
+        isempty(leftover_outputs) || @warn("The following outputs were unconnected $leftover_outputs, ignore this warning if you rely on prefix matching")
     end
 
 
@@ -657,4 +668,11 @@ for fun in [:baltrunc, :balreal]
         msys, rest... = CS.$(fun)(sys.sys, args...; kwargs...)
         named_ss(msys; sys.u, sys.y), rest...
     end
+end
+
+for fun in [:baltrunc2, :baltrunc_coprime]
+    @eval function $(fun)(sys::NamedStateSpace, args...; kwargs...)
+        msys, rest... = $(fun)(sys.sys, args...; kwargs...)
+        named_ss(msys; sys.u, sys.y), rest...
+    end
 end

src/reduction.jl

@@ -1,7 +1,7 @@
 using ControlSystemsBase: ssdata
 
 """
-    sysr, hs = frequency_weighted_reduction(G, Wo, Wi; residual=true)
+    sysr, hs = frequency_weighted_reduction(G, Wo, Wi, r=nothing; residual=true)
 
 Find Gr such that ||Wₒ(G-Gr)Wᵢ||∞ is minimized.
 For a realtive reduction, set Wo = inv(G) and Wi = I.
@@ -16,6 +16,19 @@ Ref: Andras Varga and Brian D.O. Anderson, "Accuracy enhancing methods for the f
 https://elib.dlr.de/11746/1/varga_cdc01p2.pdf
 
 Note: This function only handles exponentially stable models. To reduce unstable  and marginally stable models, decompose the system into stable and unstable parts using [`stab_unstab`](@ref), reduce the stable part and then add the unstable part back.
+
+# Example:
+The following example performs reduction with a frequency focus between frequencies `w1` and `w2`.
+```julia
+using DSP
+w1 = 1e-4
+w2 = 1e-1
+wmax = 1
+fc = DSP.analogfilter(DSP.Bandpass(w1, w2, fs=wmax), DSP.Butterworth(2))
+tfc = DSP.PolynomialRatio(fc)
+W = tf(DSP.coefb(tfc), DSP.coefa(tfc))
+rsys, hs = frequency_weighted_reduction(sys, W, 1)
+```
 """
 function frequency_weighted_reduction(G, Wo, Wi, r=nothing; residual=true, atol=sqrt(eps()), rtol=1e-3)
     iscontinuous(G) || error("Discrete systems not supported yet.")

test/test_named_systems2.jl

@@ -77,11 +77,18 @@ s2 = named_ss(G2, x = [:z], u = [:u2], y=[:y2])
     @test s12.C == G12.C
     @test s12.D == G12.D
 
-    G3 = 2*G2
-    @test ss(G3) == 2*ss(G2)
-
-    G3 = G2/2.0
-    @test ss(G3) == ss(G2)/2.0
+    G3 = 2*s2
+    @test ss(G3) == 2*ss(s2)
+    @test G3.u == s2.u
+    @test G3.y != s2.y
+
+    G3 = s2*2
+    @test ss(G3) == ss(s2)*2
+    @test G3.u != s2.u
+    @test G3.y == s2.y
+
+    G3 = s2/2.0
+    @test ss(G3) == ss(s2)/2.0
 
     @test_throws ArgumentError s1*s1
 end