[ITensors] [BUG] Itensors refuses "weight" argument to DMRG

[marcio053]

Below I'm leaving a snippet of my code that gives an error when placing the "weight" argument in the DMRG. This code works in previous versions of Itensors, but in recent versions it does not work

H=Set_Hamiltonian(sites,N,t,t1,U,e,J,K,Gamma,t0,J1,mu,dashedon)
    ############  preparing DMRM ###########
    state=InitialState(M,"Neel")
    #psi0 = productMPS(sites,state)
    psi0 = randomMPS(sites,state,linkdims = 20)

    sweeps = Sweeps(Nsweeps)

    #maxdim!(sweeps,10,20,100,200,200,200,300)
    maxdim!(sweeps,50,100,100,300)
    mindim!(sweeps,50)
    noise!(sweeps,1E-4,1E-6,1E-8,1E-8,1E-9)
    cutoff!(sweeps,1E-8)
    println("Starting DMRG")

    weight=20.0
    etol=1E-8
    obs = DemoObserver(etol)

    ############ TDVP ############    
    H1=Set_Hamiltonian(sites,N,1,1,1,1,1,1,1,1,1,0.1,true)
    maxdim=20
    println("Starting TDVP")
    tdvp!(psi0,H,0.01,0.02,maxdim=maxdim)
    println("End.")
    #########################
    #energy,psi = dmrg(H,psi0,sweeps,outputlevel=1; observer=obs, weight)
    
    energy,psi = dmrg(H,psi0,sweeps,eigsolve_krylovdim=Sweep_Niter,ishermitian=true;outputlevel
                      =output_level, weight)
                      

  ERROR: LoadError: MethodError: no method matching dmrg(::ProjMPO, ::MPS, ::Sweeps; eigsolve_krylovdim::Int64, ishermitian::Bool, outputlevel::Int64, weight::Float64)

Closest candidates are:
dmrg(::Any, ::MPS, ::Sweeps; which_decomp, svd_alg, observer, outputlevel, write_when_maxdim_exceeds, write_path, eigsolve_tol, eigsolve_krylovdim, eigsolve_maxiter, eigsolve_verbosity, eigsolve_which_eigenvalue, ishermitian) got unsupported keyword argument "weight"
@ ITensors ~/.julia/packages/ITensors/oOwvi/src/lib/ITensorMPS/src/dmrg.jl:158
dmrg(!Matched::MPO, ::MPS, ::Sweeps; kwargs...)
@ ITensors ~/.julia/packages/ITensors/oOwvi/src/lib/ITensorMPS/src/dmrg.jl:21
dmrg(!Matched::Vector{MPO}, ::MPS, ::Sweeps; kwargs...)
@ ITensors ~/.julia/packages/ITensors/oOwvi/src/lib/ITensorMPS/src/dmrg.jl:31

[emstoudenmire]

Thanks. Could you please post a minimal example that reproduces the bug? The example above includes some functions like Set_Hamiltonian and things which I don't have so I'm not able to run it.

Also, it may or may not be unrelated to the bug, but it could help to make your code in a more up-to-date style, following the code example here:
https://itensor.github.io/ITensors.jl/dev/examples/DMRG.html#Compute-excited-states-with-DMRG
Specifically note how it's preferred to no longer use the Sweeps type and instead just pass parameters like nsweeps, maxdim, etc as keyword arguments.

[mtfishman]

Also, the preferred style is using MPS instead of productMPS and random_mps instead of randomMPS, though that's unrelated to your issue.

[emstoudenmire]

I see the problem causing this error. @marcio053: the interface to dmrg that accepts the weight keyword has a different signature from the one you used above. The correct interface has the following signature:

dmrg(H::MPO, Ms::Vector{MPS}, psi0::MPS, sweeps::Sweeps; weight=true, kwargs...)

So you must pass:

• a vector of the previous MPS to orthogonalize against
• a guess or initial state for the next run of dmrg

In your case, you could call it as

energy1, psi1 dmrg(H,[psi0], psi0,sweeps,eigsolve_krylovdim=Sweep_Niter,ishermitian=true;outputlevel
                      =output_level, weight)

and that ought to work. Please let us know –