Add special interval constructors (#446)

* Add special interval constructors

* rename to zer

Author: mforets

src/IntervalArithmetic.jl

@@ -22,7 +22,7 @@ import Base:
     +, -, *, /, //, fma,
     <, >, ==, !=, ⊆, ^, <=,
     in, zero, one, eps, typemin, typemax, abs, abs2, real, min, max,
-    sqrt, exp, log, sin, cos, tan, cot, inv, cbrt, csc, hypot, sec, 
+    sqrt, exp, log, sin, cos, tan, cot, inv, cbrt, csc, hypot, sec,
     exp2, exp10, log2, log10,
     asin, acos, atan,
     sinh, cosh, tanh, coth, csch, sech, asinh, acosh, atanh, sinpi, cospi,
@@ -86,7 +86,7 @@ import Base: rounding, setrounding, setprecision
 
 ## Multidimensional
 export
-    IntervalBox
+    IntervalBox, symmetric_box
 
 ## Decorations
 export

src/multidim/intervalbox.jl

@@ -140,3 +140,19 @@ end
 
 hull(a::IntervalBox{N,T}, b::IntervalBox{N,T}) where {N,T} = IntervalBox(hull.(a[:], b[:]))
 hull(a::Vector{IntervalBox{N,T}}) where {N,T} = hull(a...)
+
+"""
+    zero(IntervalBox{N, T})
+
+Return the zero interval box of dimension `N` in the numeric type `T`.
+"""
+zero(::Type{IntervalBox{N, T}}) where {N, T} = IntervalBox(zero(Interval{T}), N)
+zero(x::IntervalBox{N, T}) where {N, T} = zero(typeof(x))
+
+"""
+    symmetric_box(N, T)
+
+Return the symmetric interval box of dimension `N` in the numeric type `T`,
+each side is `Interval(-1, 1)`.
+"""
+symmetric_box(N, ::Type{T}) where T<:Real = IntervalBox(Interval{T}(-1, 1), N)

test/interval_tests/construction.jl

@@ -370,3 +370,8 @@ import IntervalArithmetic: force_interval
     @test force_interval(Inf, -Inf) == Interval(-Inf, Inf)
     @test_throws ArgumentError force_interval(NaN, 3)
 end
+
+@testset "Zero interval" begin
+    @test zero(Interval{Float64}) === Interval{Float64}(0, 0)
+    @test zero(0 .. 1) === Interval{Float64}(0, 0)
+end

test/multidim_tests/multidim.jl

@@ -314,4 +314,10 @@ end
     @test hull(vb4) == ib4
 end
 
+@testset "Special box constructors" begin
+    @test zero(IntervalBox{2, Float64}) === IntervalBox(0 .. 0, 2)
+    @test zero((0..1) × (0..1)) === IntervalBox(0 .. 0, 2)
+    @test symmetric_box(2, Float64) === IntervalBox(-1 .. 1, 2)
+end
+
 end