add warning message in module initialization

Author: ytdHuang

src/QuantumToolbox.jl

@@ -134,4 +134,13 @@ include("visualization.jl")
 # deprecated functions
 include("deprecated.jl")
 
+# module initialization
+function __init__()
+    # this will be called immediately after the module is loaded (e.g., by import or using) at runtime for the first time.
+    # useful for announcement
+    @warn "The definition of `liouvillian` L for a given Hamiltonian H is changed to L[⋅] = -i( H[⋅] - [⋅]H' ), with ' representing complex conjugation. " *
+          "QuantumToolbox.jl no longer expects H to be Hermitian."
+    return nothing
+end
+
 end