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add additive identity element for statespace and TF #538

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Jun 12, 2021
Merged

add additive identity element for statespace and TF #538

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c786424
add additive identity element for statespace and TF
baggepinnen Jun 12, 2021
7f8da09
rm zero from type. Test MIMO zero
baggepinnen Jun 12, 2021
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2 changes: 2 additions & 0 deletions src/types/StateSpace.jl
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Expand Up @@ -217,6 +217,8 @@ function isapprox(sys1::ST1, sys2::ST2; kwargs...) where {ST1<:AbstractStateSpac
end

## ADDITION ##
Base.zero(sys::AbstractStateSpace) = ss(zero(sys.D), sys.timeevol)

function +(s1::StateSpace{TE,T}, s2::StateSpace{TE,T}) where {TE,T}
#Ensure systems have same dimensions
if size(s1) != size(s2)
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2 changes: 2 additions & 0 deletions src/types/TransferFunction.jl
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Expand Up @@ -33,6 +33,8 @@ ninputs(G::TransferFunction) = size(G.matrix, 2)
Base.ndims(::TransferFunction) = 2
Base.size(G::TransferFunction) = size(G.matrix)
Base.eltype(::Type{S}) where {S<:TransferFunction} = S
Base.zero(G::TransferFunction{TE,S}) where {TE,S} = tf(zeros(numeric_type(S), size(G)), G.timeevol) # can not create a zero of a discrete system from the type alone, the sampletime is not stored.


function Base.getindex(G::TransferFunction{TE,S}, inds...) where {TE,S<:SisoTf}
if size(inds, 1) != 2
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9 changes: 9 additions & 0 deletions test/test_connections.jl
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Expand Up @@ -83,6 +83,15 @@ s = tf("s")
vecarray(2, 1, [1,13,55,75], [1,13,55,75]));
@test parallel(Ctf_111, Ctf_211) == tf([2,17,44,45], [1,13,55,75])

# Test that the additive identity element for LTI system is known
@test zero(C_111) isa typeof(C_111)
@test zero(Ctf_111) isa typeof(Ctf_111)
@test zero(ss(randn(2,3))) == ss(zeros(2,3))
@test zero(tf(randn(2,3))) == tf(zeros(2,3))




# Combination tf and ss
@test [C_111 Ctf_221] == [C_111 ss(Ctf_221)]
@test [C_111; Ctf_212] == [C_111; ss(Ctf_212)]
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