Sparse superoperator acting on sparse operator not defined

[ericphanson]

It seems like multiplication of sparse superoperators on sparse operators is not defined. For example,

using QuantumOptics
A = GenericBasis(2)
so = spre(identityoperator(A))
ρ = basisstate(A,1) |> dm |> sparse
so * ρ 

results in

MethodError: no method matching *(::QuantumOptics.superoperators.SparseSuperOperator, ::QuantumOptics.operators_sparse.SparseOperator)
Closest candidates are:
  *(::Any, ::Any, ::Any, ::Any...) at operators.jl:424
  *(::QuantumOptics.states.Bra, ::QuantumOptics.operators.Operator) at C:\Users\Eric-d2\.julia\v0.6\QuantumOptics\src\operators_dense.jl:74
  *(::QuantumOptics.operators_dense.DenseOperator, ::QuantumOptics.operators.Operator) at C:\Users\Eric-d2\.julia\v0.6\QuantumOptics\src\operators_dense.jl:62
  ...

This seems strange!

Edit: bases.multiplicable(so,ρ) returns true in this example as well.

[david-pl]

Thanks for pointing that out. Seems like we simply missed that. I will add the function asap. In the meantime you can just add the following function which I quickly drafted to make things work:

using QuantumOptics
import Base.*

function *(a::SuperOperator, b::SparseOperator)
    QuantumOptics.superoperators.check_multiplicable(a, b)
    data = a.data*reshape(b.data, length(b.data))
    SparseOperator(a.basis_l[1], a.basis_l[2], reshape(data, length(a.basis_l[1]), length(a.basis_l[2])))
end

A = GenericBasis(2)
so = spre(identityoperator(A))
ρ = basisstate(A,1) |> dm |> sparse
so * ρ

As a remark: please be aware that sparse-sparse multiplication in Julia is currently not that efficient. So if you are planning to use this product of a superoperator and an operator in a time-critical function it might be better to leave ρ dense.

[david-pl]

I implemented the function as shown above. You can pull the latest master branch to use it (type Pkg.checkout("QuantumOptics") until a new release is drafted.