ODE updater for time independent H in TDVP

ITensor Julia Questions
1

Hi,

I want to integrate a time-independent Hamiltonian using the tdvp function of ITensorMPS.jl.
I see that there are “exponentiate” and “applyexp” updaters defined inside the tdvp function (ITensorTDVP.jl/src/tdvp.jl at main · ITensor/ITensorTDVP.jl · GitHub).

However, in the example with time-dependent Hamiltonian, an ODE solver is also implemented for the projected equations of motion. Can you help me write an ODE updater for the basic case of the time-independent Hamiltonian?

I tried to borrow the function from ITensorTDVP.jl/examples/03_updaters.jl at main · ITensor/ITensorTDVP.jl · GitHub but got incorrect results.

Best

2

I’d be happy to discuss it with you. When you tried modifying the ode_updater in the file https://github.com/ITensor/ITensorTDVP.jl/blob/main/examples/03_updaters.jl what changes did you make? I would recommend deleting the two definitions of f in there and then writing a new one that just assumes a simpler, time-independent operator is passed to the ode_updater function. Otherwise I’m not personally too familiar with the ODEProblem interface – what kind of inputs does it expect? (I did not write the 03_tdvp_time_dependent.jl example or else I would remember.)