Some usability improvements for project_traceout!() (#35)

---------

Co-authored-by: Stefan Krastanov <[email protected]>

src/backends/quantumoptics/quantumoptics.jl

@@ -37,11 +37,13 @@ function observable(state::Union{<:Ket,<:Operator}, indices, operation)
     expect(op, state)
 end
 
-function project_traceout!(state::Union{Ket,Operator},stateindex,psis::Vector{<:Ket})
+function project_traceout!(state::Union{Ket,Operator},stateindex,psis::Base.AbstractVecOrTuple{Ket})
     if nsubsystems(state) == 1 # TODO is there a way to do this in a single function, instead of _overlap vs _project_and_drop
         _overlaps = [_overlap(psi,state) for psi in psis]
         branch_probs = cumsum(_overlaps)
-        @assert branch_probs[end] ≈ 1.0
+        if !(branch_probs[end] ≈ 1.0)
+            throw("State not normalized. Could be due to passing wrong state to `initialize!`")
+        end
         j = findfirst(>=(rand()), branch_probs) # TODO what if there is numerical imprecision and sum<1
         j, nothing
     else

test/test_project_traceout.jl

@@ -27,3 +27,7 @@ for rep in [QuantumOpticsRepr(), CliffordRepr()]
     initialize!(a[1], X1)
     @test project_traceout!(a[1], σˣ) == 1
 end
+
+r = Register(1)
+initialize!(r[1], Z)
+@test_throws "State not normalized. Could be due to passing wrong state to `initialize!`" project_traceout!(r[1], (L0, L1))