Error after updating ITensors.jl

Question

Hi,

My code has an error after updating the new ITensors.jl. The sample code is as follows,

s = Index([QN(("N",i,3))=>1 for i = 0:(2)];dir = ITensors.Arrow(1))
l = setdir(addtags(s,"left"),ITensors.Arrow(-1))
r = addtags(s,"right")
A = emptyITensor(l,r)
A[l(1),r(1)] = 1.0

It throws an error saying "no method matching ValLength(::Index{Array{Pair{QN,Int64},1}})". What is changed for the new version? Thanks.

Jin

Answer 1

Hi Jin,

This works as expected for me with the latest version of ITensors.jl:

pkg> st ITensors
Status [...]
  [9136182c] ITensors v0.1.30

julia> using ITensors

julia> s = Index([QN(("N",i,3))=>1 for i = 0:(2)];dir = ITensors.Arrow(1))
(dim=3|id=859) <Out>
 1: QN("N",0,3) => 1
 2: QN("N",1,3) => 1
 3: QN("N",2,3) => 1

julia> l = setdir(addtags(s,"left"),ITensors.Arrow(-1))
(dim=3|id=859|"left") <In>
 1: QN("N",0,3) => 1
 2: QN("N",1,3) => 1
 3: QN("N",2,3) => 1

julia> r = addtags(s,"right")
(dim=3|id=859|"right") <Out>
 1: QN("N",0,3) => 1
 2: QN("N",1,3) => 1
 3: QN("N",2,3) => 1

julia> A = emptyITensor(l,r)
ITensor ord=2
(dim=3|id=859|"left") <In>
 1: QN("N",0,3) => 1
 2: QN("N",1,3) => 1
 3: QN("N",2,3) => 1
(dim=3|id=859|"right") <Out>
 1: QN("N",0,3) => 1
 2: QN("N",1,3) => 1
 3: QN("N",2,3) => 1
NDTensors.Empty{Float64,NDTensors.BlockSparse{Float64,Array{Float64,1},2}}

julia> A[l(1),r(1)] = 1.0
1.0

julia> @show A;
A = ITensor ord=2
Dim 1: (dim=3|id=859|"left") <In>
 1: QN("N",0,3) => 1
 2: QN("N",1,3) => 1
 3: QN("N",2,3) => 1
Dim 2: (dim=3|id=859|"right") <Out>
 1: QN("N",0,3) => 1
 2: QN("N",1,3) => 1
 3: QN("N",2,3) => 1
NDTensors.BlockSparse{Float64,Array{Float64,1},2}
 3×3
Block: Block{2}((0x0000000000000001, 0x0000000000000001), 0xa03b74afc6984a6a)
 [1:1, 1:1]
 1.0

We've been making quite a few changes to indexing and block sparse operations in recent versions, so possibly something broke in one of the versions before v0.1.30.

Also note that the Index direction is out by default, and you can make a new Index with the arrow direction reversed with dag:

julia> s = Index([QN("N",i,3)=>1 for i = 0:2])
(dim=3|id=917) <Out>
 1: QN("N",0,3) => 1
 2: QN("N",1,3) => 1
 3: QN("N",2,3) => 1

julia> l = dag(addtags(s,"left"))
(dim=3|id=917|"left") <In>
 1: QN("N",0,3) => 1
 2: QN("N",1,3) => 1
 3: QN("N",2,3) => 1

-Matt

Comments

Ah I see, indeed when I go back to v0.1.29 of ITensors.jl I see the same error as you. Please update to v0.1.30 with:

    julia> using Pkg; Pkg.update()

or equivalently:

    julia> ] up

---

It appears that the issue is particular to having v0.1.29 of ITensors.jl and v0.1.19 of NDTensors.jl, I can make it more strict in the future about which versions are compatible with which. So an alternative is to set ITensors.jl to v0.1.29 and NDTensors.jl to v0.1.18 (in case someone is having trouble with the latest versions).

---

Thanks Matt, very helpful.