[julia] DMRGObserver not working

Question

Hello,

I'm new to ITensors and try to mainly use the DMRG features here. I found the DMRGObserver feature pretty useful and was trying to implement it according to the documentation here . However, I saw an error while trying to create the DMRGObserver.

DMRGObserver(energy_tol = 1e-5, minsweeps = 2)

The error reads:

    ERROR: MethodError: no method matching DMRGObserver(; energy_tol=1.0e-5, minsweeps=2)
Closest candidates are:
  DMRGObserver() at C:\Users\Sherry\.julia\packages\ITensors\2Rd6c\src\mps\observer.jl:33 got unsupported keyword arguments "energy_tol", "minsweeps"
  DMRGObserver(::Array{String,1}, ::Array{var"#s305",1} where var"#s305"<:Index; energy_tol, minsweeps) at C:\Users\Sherry\.julia\packages\ITensors\2Rd6c\src\mps\observer.jl:38
  DMRGObserver(::Any) at C:\Users\Sherry\.julia\packages\ITensors\2Rd6c\src\mps\observer.jl:33 got unsupported keyword arguments "energy_tol", "minsweeps"

Then I simply tried DMRGObserver(), still it gives the error

ERROR: MethodError: no method matching Array{var"#s305",1} where var"#s305"<:Index(::Array{Any,1})
Stacktrace:
 [1] convert(::Type{Array{var"#s305",1} where var"#s305"<:Index}, ::Array{Any,1}) at .\array.jl:554
 [2] DMRGObserver(::Float64, ::Int64) at C:\Users\Sherry\.julia\packages\ITensors\2Rd6c\src\mps\observer.jl:35 (repeats 2 times)
 [3] top-level scope at REPL[8]:1

I'm using the most up-to-date version of ITensors (0.1.34). I don't have a good idea on how to fix it from here on. Please let me know if you have any suggestions.

Thanks,
Sherry

Answer 1

Hi Sherry, so that documentation was a little bit hard to understand, because it makes it appear as if those arguments are named arguments. They are (or were - see below) not named arguments but just default arguments. However, that constructor turned out to have another bug, so would not have worked anyway even if called correctly.

I used that situation as an opportunity to improve the interface, and now it should work as you'd expect, i.e.

DMRGObserver(; energy_tol = 1E-4, minsweeps = 2)

say. Note that this is true right now only for the master branch of ITensors.jl and isn't in the latest numbered version yet. But we will tag a new version soon and the change will be included in 0.1.35.

Miles

Comments

Hi Miles,

I see. Now I use a similar construction function as the example and it works. Initially, I just wanted to use it to set a stop criterion without measuring any observables. Seems like for now I have to put some observable and sites here in order to use it?

Thanks,
Sherry

---

Yes, that's correct if by "for now" you mean for version 0.1.34 of ITensors. But we are tagging a new version 0.1.35 currently that should be available by tomorrow at the latest, and then you can use the more basic DMRGObserver constructor too.

Miles