Merge pull request #2479 from JuliaReach/schillic/isdisjoint

Fix bug in isdisjoint of two zonotopic sets

src/ConcreteOperations/isdisjoint.jl

@@ -482,7 +482,7 @@ witness.
 
 ### Algorithm
 
-``Z1 ∩ Z2 ≠ ∅`` iff ``c_1 - c_2 ∈ Z(0, (g_1, g_2))`` where ``c_i`` and ``g_i``
+``Z1 ∩ Z2 = ∅`` iff ``c_1 - c_2 ∉ Z(0, (g_1, g_2))`` where ``c_i`` and ``g_i``
 are the center and generators of zonotope `Zi` and ``Z(c, g)`` represents the
 zonotope with center ``c`` and generators ``g``.
 """
@@ -492,7 +492,7 @@ function is_intersection_empty(Z1::AbstractZonotope, Z2::AbstractZonotope,
     @assert n == dim(Z2) "zonotopes need to have the same dimensions"
     N = promote_type(eltype(Z1), eltype(Z2))
     Z = Zonotope(zeros(N, n), hcat(genmat(Z1), genmat(Z2)))
-    result = (center(Z1) - center(Z2)) ∈ Z
+    result = (center(Z1) - center(Z2)) ∉ Z
     if result
         return witness ? (true, N[]) : true
     elseif witness

test/unit_Zonotope.jl

@@ -301,23 +301,22 @@ for N in [Float64]
 
     gens = N[1 1; -1 1]
     Z1 = Zonotope(N[1, 1], gens)
-    Z2 = Zonotope(N[-1, 1], Matrix{N}(I, 2, 2))
-    Z3 = minkowski_sum(Z1, Z2)
+    Z2 = Zonotope(N[-2, -1], Matrix{N}(I, 2, 2))
 
-    # intersection with a hyperplane
+    # isdisjoint with a hyperplane
     H1 = Hyperplane(N[1, 1], N(3))
     intersection_empty, point = is_intersection_empty(Z1, H1, true)
-    @test point ∈ Z1 && point ∈ H1
+    @test !intersection_empty && point ∈ Z1 && point ∈ H1
     # zonotope without generators (#2204)
     Z3 = Zonotope(N[0, 0], Matrix{N}(undef, 2, 0))
     @test isdisjoint(Z3, H1)
 
-    # isdisjoint
+    # isdisjoint with another zonotope
     result, w = isdisjoint(Z1, Z2, true)
     @test isdisjoint(Z1, Z2) && result && w == N[]
     Z3 = Zonotope(N[2, 1], Matrix{N}(I, 2, 2))
-    @test_throws ErrorException isdisjoint(Z2, Z3, true)
-    @test !isdisjoint(Z2, Z3)
+    @test_throws ErrorException isdisjoint(Z1, Z3, true)
+    @test !isdisjoint(Z1, Z3)
 
     # issubset
     Z = Zonotope(N[0, 0], N[1 1; -1 1])