SimpleSparsePolynomialZonotope

SimpleSparsePolynomialZonotope{N, VN<:AbstractVector{N},
                               MN<:AbstractMatrix{N},
                               ME<:AbstractMatrix{Int}}
    <: AbstractSparsePolynomialZonotope{N}

Type that represents a sparse polynomial zonotope that is simple in the sense that there is no distinction between independent and dependent generators.

A simple sparse polynomial zonotope $\mathcal{PZ} ⊂ ℝ^n$ is represented by the set

\[\mathcal{PZ} = \left\{x ∈ ℝ^n : x = c + ∑_{i=1}^h \left(∏_{k=1}^p α_k^{E_{k, i}} \right) g_i,~~ α_k ∈ [-1, 1]~~ ∀ i = 1,…,p \right\},\]

where $c ∈ ℝ^n$ is the offset vector (or center), $G ∈ ℝ^{n × h}$ is the generator matrix with columns $g_i$ (each $g_i$ is called a generator), and where $E ∈ \mathbb{N}^{p×h}_{≥0}$ is the exponent matrix with matrix elements $E_{k, i}$.

Fields

• c – offset vector
• G – generator matrix
• E – exponent matrix

Notes

Sparse polynomial zonotopes were introduced in Kochdumper and Althoff [KA21]. The simple variant was defined in [Kochdumper21b].

convex_hull(X::LazySet)

Compute the convex hull of a set.

Input

• X – set

Output

A set representing the convex hull of X.

Notes

The convex hull of a set $X$ is defined as

\[ \{λx + (1-λ)y \mid x, y ∈ X, λ ∈ [0, 1]\}.\]

Extended help

convex_hull(P::SimpleSparsePolynomialZonotope)

Output

The tightest convex simple sparse polynomial zonotope containing P.

expmat(P::SimpleSparsePolynomialZonotope)

Return the matrix of exponents of a simple sparse polynomial zonotope.

Input

• P – simple sparse polynomial zonotope

Output

The matrix of exponents, where each column is a multidegree.

Notes

In the exponent matrix, each row corresponds to a parameter ($lpha_k$ in the mathematical set definition) and each column corresponds to a monomial.

Examples

julia> S = SimpleSparsePolynomialZonotope([2.0, 0], [1 2;2 2.], [1 4;1 2])
SimpleSparsePolynomialZonotope{Float64, Vector{Float64}, Matrix{Float64}, Matrix{Int64}}([2.0, 0.0], [1.0 2.0; 2.0 2.0], [1 4; 1 2])

julia> expmat(S)
2×2 Matrix{Int64}:
 1  4
 1  2

ngens(Z::AbstractZonotope)

Return the number of generators of a zonotopic set.

Input

• Z – zonotopic set

Output

An integer representing the number of generators.

Extended help

ngens(P::SimpleSparsePolynomialZonotope)

Notes

This number corresponds to the number of monomials in the polynomial representation of P.

rand(T::Type{<:LazySet}; [N]::Type{<:Real}=Float64, [dim]::Int=2,
     [rng]::AbstractRNG=GLOBAL_RNG, [seed]::Union{Int, Nothing}=nothing
    )

Create a random set of the given set type.

Input

• T – set type
• N – (optional, default: Float64) numeric type
• dim – (optional, default: 2) dimension
• rng – (optional, default: GLOBAL_RNG) random number generator
• seed – (optional, default: nothing) seed for reseeding

Output

A random set of the given set type.

Extended help

rand(::Type{SimpleSparsePolynomialZonotope};
     [N]::Type{<:Real}=Float64, [dim]::Int=2, [nparams]::Int=2,
     [maxdeg]::Int=3, [num_generators]::Int=-1,
     [rng]::AbstractRNG=GLOBAL_RNG, [seed]::Union{Int, Nothing}=nothing)

Algorithm

All numbers are normally distributed with mean 0 and standard deviation 1.

The number of generators can be controlled with the argument num_generators. For a negative value we choose a random number in the range dim:2*dim (except if dim == 1, in which case we only create a single generator). Note that the final number of generators may be lower if redundant monomials are generated.

remove_redundant_generators(Z::AbstractZonotope)

Remove all redundant (pairwise linearly dependent) generators of a zonotopic set.

Input

• Z – zonotopic set

Output

A new zonotope with fewer generators, or the same zonotopic set if no generator could be removed.

Algorithm

By default this implementation returns the input zonotopic set. Subtypes of AbstractZonotope whose generators can be removed have to define a new method.

remove_redundant_generators(S::SimpleSparsePolynomialZonotope)

Remove redundant generators from a simple sparse polynomial zonotope.

Input

• S – simple sparse polynomial zonotope

Output

A new simple sparse polynomial zonotope such that redundant generators have been removed.

Notes

The result uses dense arrays irrespective of the array type of S.

Algorithm

Let G be the generator matrix and E the exponent matrix of S. The following simplifications are performed:

• Zero columns in G and the corresponding columns in E are removed.
• For zero columns in E, the corresponding column in G is summed to the center.
• Repeated columns in E are grouped together by summing the corresponding columns in G.

quadratic_map(Q::Vector{<:AbstractMatrix}, S::SimpleSparsePolynomialZonotope)

Return the quadratic map of a simple sparse polynomial zonotope.

Input

• Q – vector of square matrices
• S – simple sparse polynomial zonotope

Output

The quadratic map of P represented as a simple sparse polynomial zonotope.

Algorithm

This method implements Kochdumper and Althoff [KA21], Proposition 12. See also Kochdumper [Koc22], Proposition 3.1.30.

quadratic_map(Q::Vector{<:AbstractMatrix}, S1::SimpleSparsePolynomialZonotope,
              S2::SimpleSparsePolynomialZonotope)

Return the quadratic map of two simple sparse polynomial zonotopes. The quadratic map is the set

\[ \{x \mid xᵢ = s₁ᵀQᵢs₂, s₁ ∈ S₁, s₂ ∈ S₂, Qᵢ ∈ Q\}.\]

Input

• Q – vector of square matrices
• S1 – simple sparse polynomial zonotope
• S2 – simple sparse polynomial zonotope

Output

The quadratic map of the given simple sparse polynomial zonotopes represented as a simple sparse polynomial zonotope.

Algorithm

This method implements Kochdumper [Koc22], Proposition 3.1.30.

cartesian_product(X::LazySet, Y::LazySet)

Compute the Cartesian product of two sets.

Input

• X – set
• Y – set

Output

A set representing the Cartesian product $X × Y$.

Notes

The Cartesian product of two sets $X$ and $Y$ is defined as

\[ X × Y = \{[x, y] \mid x ∈ X, y ∈ Y\}.\]

Extended help

cartesian_product(P1::SimpleSparsePolynomialZonotope,
                  P2::SimpleSparsePolynomialZonotope)

Algorithm

This method implements Kochdumper [Koc22], Proposition 3.1.22.

linear_combination(X::LazySet, Y::LazySet)

Compute the linear combination of two sets.

Input

• X – set
• Y – set

Output

A set representing the linear combination of X and Y.

Notes

The linear combination of two sets $X$ and $Y$ is defined as

\[ \left\{\frac{1}{2}(1+λ)x + \frac{1}{2}(1-λ)y \mid x ∈ X, y ∈ Y, λ ∈ [-1, 1]\right\}.\]

If $X$ and $Y$ are convex, their linear combination is identical with the convex hull of their union $X ∪ Y$.

Extended help

linear_combination(P1::SimpleSparsePolynomialZonotope,
                   P2::SimpleSparsePolynomialZonotope)

Notes

This method implements the algorithm described in Kochdumper [Koc22], Proposition 3.1.25.