add_output for named ss

src/named_systems2.jl

@@ -363,7 +363,9 @@ end
 """
     measure(s::NamedStateSpace, names)
 
-Return a system with specified states as measurement outputs.
+Return a system with specified state variables as measurement outputs.
+
+See also [`add_output`](@ref).
 """
 function measure(s::NamedStateSpace, names)
     inds = names2indices(names, s.x)
@@ -840,6 +842,27 @@ function CS.append(systems::NamedStateSpace...; kwargs...)
 end
 
 
+"""
+    add_output(sys::NamedStateSpace, C2::AbstractArray, D2 = 0; y)
+
+Add outputs to `sys` corresponding to the output matrix `C2` and the feedthrough matrix `D2` to the system `sys`.
+
+# Arguments:
+- `y`: The names used for the new outputs. If not provided, the names will be generated automatically.
+
+See also [`measure`](@ref) for a simpler way to output state variables.
+"""
+function CS.add_output(sys::NamedStateSpace, C2::AbstractArray, D2=0; y = [Symbol("y_$i") for i in (1:size(C2, 1)) .+ sys.ny])
+    T = promote_type(CS.numeric_type(sys), eltype(C2), eltype(D2))
+    A,B,C,D = ssdata(sys)
+    D3 = D2 == 0 ? zeros(T, size(C2, 1), sys.nu) : D2
+    x = sys.x
+    u = sys.u
+    y = [sys.y; y]
+    named_ss(ss(A, B, [C; C2], [D; D3]), sys.timeevol; x, u, y)
+end
+
+
 function CS.minreal(sys::NamedStateSpace, args...; kwargs...)
     msys = minreal(sys.sys, args...; kwargs...)
     named_ss(msys; sys.u, sys.y, sys.name)

test/test_named_systems2.jl

@@ -139,6 +139,10 @@ end
     G = measure(s1, :x)
     @test G.C == ones(1, 1)
     @test G.y == [:x]
+
+    @test add_output(s1, [0.2]) isa NamedStateSpace
+    @test add_output(s1, [0.2], y=[:hej]).y[2] === :hej
+
 end
 
 G1 = ss(1,1,1,0)