fix stack overflow error in QobjEvo multiplication

Author: ytdHuang

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased](https://github.com/qutip/QuantumToolbox.jl/tree/main)
 
 - Improve Bloch sphere rendering for animation. ([#520])
+- Fix stack overflow error in `QobjEvo` multiplication. ([#524], [#525])
 
 ## [v0.34.0]
 Release date: 2025-07-29
@@ -295,3 +296,5 @@ Release date: 2024-11-13
 [#515]: https://github.com/qutip/QuantumToolbox.jl/issues/515
 [#517]: https://github.com/qutip/QuantumToolbox.jl/issues/517
 [#520]: https://github.com/qutip/QuantumToolbox.jl/issues/520
+[#524]: https://github.com/qutip/QuantumToolbox.jl/issues/524
+[#525]: https://github.com/qutip/QuantumToolbox.jl/issues/525

src/qobj/arithmetic_and_attributes.jl

@@ -42,11 +42,22 @@ for op in (:(+), :(-), :(*))
             return QType($(op)(A.data, B.data), A.type, A.dimensions)
         end
         Base.$op(A::AbstractQuantumObject) = get_typename_wrapper(A)($(op)(A.data), A.type, A.dimensions)
+    end
 
-        Base.$op(n::T, A::AbstractQuantumObject) where {T<:Number} =
-            get_typename_wrapper(A)($(op)(n * I, A.data), A.type, A.dimensions)
-        Base.$op(A::AbstractQuantumObject, n::T) where {T<:Number} =
-            get_typename_wrapper(A)($(op)(A.data, n * I), A.type, A.dimensions)
+    if op == :(*)
+        @eval begin
+            Base.$op(n::T, A::AbstractQuantumObject) where {T<:Number} =
+                get_typename_wrapper(A)($(op)(n, A.data), A.type, A.dimensions)
+            Base.$op(A::AbstractQuantumObject, n::T) where {T<:Number} =
+                get_typename_wrapper(A)($(op)(A.data, n), A.type, A.dimensions)
+        end
+    else
+        @eval begin
+            Base.$op(n::T, A::AbstractQuantumObject) where {T<:Number} =
+                get_typename_wrapper(A)($(op)(n * I, A.data), A.type, A.dimensions)
+            Base.$op(A::AbstractQuantumObject, n::T) where {T<:Number} =
+                get_typename_wrapper(A)($(op)(A.data, n * I), A.type, A.dimensions)
+        end
     end
 end
 

test/core-test/quantum_objects_evo.jl

@@ -70,15 +70,18 @@
     end
 
     @testset "arithmetic" begin
-        a = MatrixOperator(sprand(ComplexF64, 100, 100, 0.1))
+        m = sprand(ComplexF64, 100, 100, 0.1)
+        a = MatrixOperator(m)
         a2 = QobjEvo(a)
         a3 = QobjEvo(a, type = SuperOperator())
+        a4 = QobjEvo(Qobj(m), (p, t) -> 1)
 
         @test +a2 == a2
         @test -(-a2) == a2
         @test a2 + 2 == 2 + a2
         @test (a2 + 2).data == a2.data + 2 * I
         @test a2 * 2 == 2 * a2
+        @test 1*a*a*1 == 1*(a*a) == (a*a)*1 == 1*(a*a)*1 # to check QobjEvo multiplication with Number is correct
 
         zero_like = zero(a2)
         iden_like = one(a3)