#58 - added common functions for SingleSet

src/SingleSet.jl

@@ -1,4 +1,5 @@
-export SingleSet
+export SingleSet,
+       element
 
 """
     SingleSet{N<:Real} <: Box{N}

src/Singleton.jl

@@ -15,6 +15,41 @@ struct Singleton{N<:Real} <: SingleSet{N}
     element::Vector{N}
 end
 
+"""
+    element(S::Singleton{N})::Vector{N} where {N<:Real}
+
+Return the element of a singleton.
+
+### Input
+
+- `S` -- singleton
+
+### Output
+
+The element of the singleton.
+"""
+function element(S::Singleton{N})::Vector{N} where {N<:Real}
+    return S.element
+end
+
+"""
+    element(S::Singleton{N}, i::Int)::N where {N<:Real}
+
+Return the i-th entry of the element of a singleton.
+
+### Input
+
+- `S` -- singleton
+- `i` -- dimension
+
+### Output
+
+The i-th entry of the element of the singleton.
+"""
+function element(S::Singleton{N}, i::Int)::N where {N<:Real}
+    return S.element[i]
+end
+
 """
     dim(S::Singleton)::Int
 

src/ZeroSet.jl

@@ -17,6 +17,41 @@ end
 # type-less convenience constructor
 ZeroSet(dim::Int) = ZeroSet{Float64}(dim)
 
+"""
+    element(S::ZeroSet{N})::Vector{N} where {N<:Real}
+
+Return the element of a zero set.
+
+### Input
+
+- `S` -- zero set
+
+### Output
+
+The element of the zero set, i.e., a zero vector.
+"""
+function element(S::ZeroSet{N})::Vector{N} where {N<:Real}
+    return zeros(N, S.dim)
+end
+
+"""
+    element(S::ZeroSet{N}, ::Int)::N where {N<:Real}
+
+Return the i-th entry of the element of a zero set.
+
+### Input
+
+- `S` -- zero set
+- `i` -- dimension
+
+### Output
+
+The i-th entry of the element of the zero set, i.e., 0.
+"""
+function element(S::ZeroSet{N}, ::Int)::N where {N<:Real}
+    return zero(N)
+end
+
 """
     dim(Z::ZeroSet)::Int