Merge pull request #283 from JuliaReach/schillic/pow

Fix `pow`/`pown` error

Author: schillic

src/init_IntervalArithmetic.jl

@@ -21,6 +21,8 @@ else  # vIA < v"0.22"
 
     intersect_interval(a::Interval, b::Interval) = intersect(a, b)
 
+    pown(x, y) = x^y
+
     if vIA >= v"0.21"
         # `convert` was temporarily removed in IntervalArithmetic v0.21 until v0.22
         Base.convert(::Type{Interval{T}}, x::Number) where {T} = interval(T(x))

src/operations/arithmetic.jl

@@ -83,7 +83,7 @@ function square(A::IntervalMatrix)
 
     # case i == j
     @inbounds for j in 1:n
-        B[j, j] = pow(A[j, j], 2)
+        B[j, j] = pown(A[j, j], 2)
         for k in 1:n
             k == j && continue
             B[j, j] += A[j, k] * A[k, j]

test/exponential.jl

@@ -60,6 +60,10 @@ end
     a = m * m
     b = square(m)
     @test b ⊆ a
+
+    # correct use of `pown` (#283)
+    m = IntervalMatrix(hcat(interval(-4.0, -2.0)))
+    @test square(m) ⩵ IntervalMatrix(hcat(interval(4.0, 16.0)))
 end
 
 @testset "Interval matrix power" begin