Add IntervalBox constructor from vectors giving opposite corners (#238)

* Add IntervalBox constructor from corners of box

* Force the interval even if the bounds are the wrong way round

* Add test

* Allow arbitrary AbstractVectors for construction of IntervalBox from corners

* (Re-)add fast version for creating IntervalBox from two equal length SVectors

* Move force_interval to intervals.jl and add tests

* Fix extra end

Author: dpsanders

src/intervals/intervals.jl

@@ -109,6 +109,12 @@ end
 interval(a::Real) = interval(a, a)
 interval(a::Interval) = a
 
+"Make an interval even if a > b"
+function force_interval(a, b)
+    a > b && return interval(b, a)
+    return interval(a, b)
+end
+
 
 ## Include files
 include("special.jl")

src/multidim/intervalbox.jl

@@ -17,6 +17,12 @@ IntervalBox(x...) = IntervalBox(x)
 IntervalBox(x) = IntervalBox(x...)
 IntervalBox(X::IntervalBox, n) = foldl(×, Iterators.repeated(X, n))
 
+# construct from two vectors giving bottom and top corners:
+IntervalBox(lo::AbstractVector, hi::AbstractVector) where {N,T} = IntervalBox(force_interval.(lo, hi))
+
+IntervalBox(lo::SVector{N,T}, hi::SVector{N,T}) where {N,T} = IntervalBox(force_interval.(lo, hi))
+
+
 Base.@propagate_inbounds Base.getindex(X::IntervalBox, i) = X.v[i]
 
 setindex(X::IntervalBox, y, i) = IntervalBox( setindex(X.v, y, i) )

test/interval_tests/construction.jl

@@ -331,3 +331,12 @@ end
     @test !isequal(hash(x), hash(y))
 
 end
+
+import IntervalArithmetic: force_interval
+@testset "force_interval" begin
+    @test force_interval(4, 3) == Interval(3, 4)
+    @test force_interval(4, Inf) == Interval(4, Inf)
+    @test force_interval(Inf, 4) == Interval(4, Inf)
+    @test force_interval(Inf, -Inf) == Interval(-Inf, Inf)
+    @test_throws ArgumentError force_interval(NaN, 3)
+end

test/multidim_tests/multidim.jl

@@ -191,6 +191,10 @@ end
     @test IntervalBox([1:5...]) == IntervalBox(1..1, 2..2, 3..3, 4..4, 5..5)
     @test IntervalBox((1..2) × (2..3), 2) == (1..2) × (2..3) × (1..2) × (2..3)
 
+    # construct from corners:
+    @test IntervalBox(SVector(1, 2), SVector(3, 4)) == (1..3) × (2..4)
+    @test IntervalBox(SVector(3, 4), SVector(1, 2)) == (1..3) × (2..4)
+
 end
 
 @testset "getindex and setindex" begin