Add constrained_dimensions method for HPolyhedron

docs/src/lib/representations.md

@@ -442,7 +442,6 @@ vertices_list(::HPolytope{N}) where {N<:Real}
 
 Inherited from [`AbstractPolytope`](@ref):
 * [`singleton_list`](@ref singleton_list(::AbstractPolytope{N}) where {N<:Real})
-The following methods are specific for polytopes.
 
 #### Polyhedra
 
@@ -452,6 +451,7 @@ The following methods are specific for `HPolyhedron`.
 rand(::Type{HPolyhedron})
 vertices_list(::HPolyhedron{N}) where {N<:Real}
 singleton_list(::HPolyhedron{N}) where {N<:Real}
+constrained_dimensions(::HPolyhedron{N}) where {N<:Real}
 ```
 
 ### Vertex representation

src/HPolyhedron.jl

@@ -17,7 +17,8 @@ export HPolyhedron,
        singleton_list,
        isempty,
        remove_redundant_constraints,
-       remove_redundant_constraints!
+       remove_redundant_constraints!,
+       constrained_dimensions
 
 """
     HPolyhedron{N<:Real} <: LazySet{N}
@@ -247,6 +248,35 @@ function rand(::Type{HPolyhedron};
     return HPolyhedron(constraints_Q)
 end
 
+"""
+    constrained_dimensions(P::HPolyhedron{N})::Vector{Int} where {N<:Real}
+
+Return the indices in which a polyhedron in constraint representation is
+constrained.
+
+### Input
+
+- `P` -- polyhedron in constraint representation
+
+### Output
+
+A vector of ascending indices `i` such that the polyhedron is constrained in
+dimension `i`.
+
+### Examples
+
+A 2D polyhedron with constraint ``x1 ≥ 0`` is constrained in dimension 1 only.
+"""
+function constrained_dimensions(P::HPolyhedron{N})::Vector{Int} where {N<:Real}
+    zero_indices = zeros(Int, dim(P))
+    for constraint in P.constraints
+        for i in constrained_dimensions(constraint)
+            zero_indices[i] = i
+        end
+    end
+    return filter(x -> x != 0, zero_indices)
+end
+
 
 # ===========================================
 # HPolyhedron and HPolytope's shared methods

src/HalfSpace.jl

@@ -210,7 +210,7 @@ Return the indices in which a half-space is constrained.
 A vector of ascending indices `i` such that the half-space is constrained in
 dimension `i`.
 
-### Notes
+### Examples
 
 A 2D half-space with constraint ``x1 ≥ 0`` is constrained in dimension 1 only.
 """

src/Hyperplane.jl

@@ -182,7 +182,7 @@ Return the indices in which a hyperplane is constrained.
 A vector of ascending indices `i` such that the hyperplane is constrained in
 dimension `i`.
 
-### Notes
+### Examples
 
 A 2D hyperplane with constraint ``x1 = 0`` is constrained in dimension 1 only.
 """

src/Line.jl

@@ -248,7 +248,7 @@ Return the indices in which a line is constrained.
 A vector of ascending indices `i` such that the line is constrained in dimension
 `i`.
 
-### Notes
+### Examples
 
 A line with constraint ``x1 = 0`` is constrained in dimension 1 only.
 """

test/unit_Polyhedron.jl

@@ -45,6 +45,11 @@ for N in [Float64, Rational{Int}, Float32]
     @test ∈(N[5 / 4, 7 / 4], p)
     @test !∈(N[4, 1], p)
 
+    # constrained dimensions
+    @test constrained_dimensions(p) == [1, 2]
+    @test constrained_dimensions(
+        HPolyhedron{N}([LinearConstraint(N[1, 0], N(1))])) == [1]
+
     if test_suite_polyhedra
         # conversion to and from Polyhedra's VRep data structure
         cl = constraints_list(HPolyhedron(polyhedron(p)))