Merge pull request #1528 from JuliaReach/schillic/422

#422 - Require non-zero normal directions in Line/Hyperplane/HalfSpace
JuliaReach · Jul 27, 2019 · 5cc0310 · 5cc0310
2 parents 786611d + 01aa37a
commit 5cc0310
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Showing 6 changed files with 31 additions and 4 deletions.
diff --git a/src/HalfSpace.jl b/src/HalfSpace.jl
@@ -15,7 +15,7 @@ Type that represents a (closed) half-space of the form ``a⋅x ≤ b``.
 
 ### Fields
 
-- `a` -- normal direction
+- `a` -- normal direction (non-zero)
 - `b` -- constraint
 
 ### Examples
@@ -30,8 +30,18 @@ HalfSpace{Float64,Array{Float64,1}}([0.0, -1.0], 0.0)
 struct HalfSpace{N<:Real, VN<:AbstractVector{N}} <: AbstractPolyhedron{N}
     a::VN
     b::N
+
+    function HalfSpace{N, VN}(a::VN, b::N
+                             ) where {N<:Real, VN<:AbstractVector{N}}
+        @assert !iszero(a) "a half-space needs a non-zero normal vector"
+        return new{N, VN}(a, b)
+    end
 end
 
+# convenience constructor without type parameter
+HalfSpace(a::VN, b::N) where {N<:Real, VN<:AbstractVector{N}} =
+    HalfSpace{N, VN}(a, b)
+
 """
     LinearConstraint
 

diff --git a/src/Hyperplane.jl b/src/Hyperplane.jl
@@ -12,7 +12,7 @@ Type that represents a hyperplane of the form ``a⋅x = b``.
 
 ### Fields
 
-- `a` -- normal direction
+- `a` -- normal direction (non-zero)
 - `b` -- constraint
 
 ### Examples
@@ -27,8 +27,16 @@ Hyperplane{Float64}([0.0, 1.0], 0.0)
 struct Hyperplane{N<:Real} <: AbstractPolyhedron{N}
     a::AbstractVector{N}
     b::N
+
+    function Hyperplane{N}(a::AbstractVector{N}, b::N) where {N<:Real}
+        @assert !iszero(a) "a hyperplane needs a non-zero normal vector"
+        return new{N}(a, b)
+    end
 end
 
+# convenience constructor without type parameter
+Hyperplane(a::AbstractVector{N}, b::N) where {N<:Real} = Hyperplane{N}(a, b)
+
 
 # --- polyhedron interface functions ---
 

diff --git a/src/Line.jl b/src/Line.jl
@@ -13,7 +13,7 @@ of a `Hyperplane`).
 
 ### Fields
 
-- `a` -- normal direction
+- `a` -- normal direction (non-zero)
 - `b` -- constraint
 
 ### Examples
@@ -32,7 +32,7 @@ struct Line{N<:Real, VN<:AbstractVector{N}} <: AbstractPolyhedron{N}
     # default constructor with length constraint
     function Line{N, VN}(a::VN, b::N) where {N<:Real, VN<:AbstractVector{N}}
         @assert length(a) == 2 "lines must be two-dimensional"
-        @assert a != zeros(N, 2) "the normal vector of a line must not be zero"
+        @assert !iszero(a) "a line needs a non-zero normal vector"
         return new{N, VN}(a, b)
     end
 end

diff --git a/test/unit_HalfSpace.jl b/test/unit_HalfSpace.jl
@@ -5,6 +5,9 @@ for N in [Float64, Rational{Int}, Float32]
     # normal constructor
     hs = HalfSpace(ones(N, 3), N(5))
 
+    # corner case: zero normal vector
+    @test_throws AssertionError HalfSpace(N[0, 0], N(1))
+
     # dimension
     @test dim(hs) == 3
 

diff --git a/test/unit_Hyperplane.jl b/test/unit_Hyperplane.jl
@@ -7,6 +7,9 @@ for N in [Float64, Rational{Int}, Float32]
     b = N(5)
     hp = Hyperplane(a, b)
 
+    # corner case: zero normal vector
+    @test_throws AssertionError Hyperplane(N[0, 0], N(1))
+
     # dimension
     @test dim(hp) == 3
 

diff --git a/test/unit_Line.jl b/test/unit_Line.jl
@@ -25,6 +25,9 @@ for N in [Float64, Rational{Int}, Float32]
           [1.0, 10.0] ∈ L
           [10.0, 10.0] ∉ L
 
+    # corner case: zero normal vector
+    @test_throws AssertionError Line(N[0, 0], N(1))
+
     # dimension
     @test dim(l1) == 2