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Let 1D linear_map of zonotopic set remove redudant generator #3764

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Let 1D linear_map of zonotopic set remove redudant generator #3764

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7 changes: 4 additions & 3 deletions src/Interfaces/AbstractZonotope.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -304,8 +304,8 @@ A `Zonotope`.

We apply the linear map to the center and the generators.

If the map has outpu dimension 1, a specialized algorithm ensures that the
resulting zonotope only has a single generator.
If the map has output dimension 1, a specialized algorithm ensures that the
resulting zonotope only has a single generator (or none if the map is zero).
"""
function linear_map(M::AbstractMatrix, Z::AbstractZonotope)
@assert dim(Z) == size(M, 2) "a linear map of size $(size(M)) cannot be " *
Expand All @@ -326,7 +326,8 @@ function _linear_map_zonotope_1D(M::AbstractMatrix, Z::LazySet)
@inbounds for g in generators(Z)
gi += abs(sum(M[1, i] * g[i] for i in eachindex(g)))
end
return Zonotope(c, hcat(gi))
G = iszero(gi) ? Matrix{N}(undef, 1, 0) : hcat(gi)
return Zonotope(c, G)
end

function _linear_map_zonotope_nD(M::AbstractMatrix, Z::LazySet)
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4 changes: 4 additions & 0 deletions test/Sets/Zonotope.jl
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Expand Up @@ -112,6 +112,10 @@ for N in [Float64, Rational{Int}, Float32]
M = N[-1 1;]
Z6 = linear_map(M, Z3)
@test ngens(Z6) == 1 && genmat(Z6) == hcat(N[4])
# ... unless the map is zero
M = N[0 0;]
Z7 = linear_map(M, Z3)
@test ngens(Z7) == 0 && genmat(Z7) == Matrix{N}(undef, 1, 0)

# in-place linear map
Zin = convert(Zonotope, BallInf(zeros(N, 2), N(1)))
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