[Julia] QN Block Sparse ITensor gives wrong results for multiplying the delta tensor

Question

Hi,

For the following code, the answer should be "4.0", but it gives "2.0". Maybe it is a bug. Thanks.

s = Index([QN(("N",i,1))=>1 for i = 1:2];dir = ITensors.Arrow(1))
l = dag(addtags(s,"left"))
r = addtags(s,"right")
u = addtags(s,"up")
d = dag(addtags(s,"down"))
A = emptyITensor(l,r,u,d)
A[1,1,1,1] = 1.0
A[1,1,2,2] = 1.0
A[2,2,1,1] = 1.0
A[2,2,2,2] = 1.0
println(A*delta(dag(l),dag(r))*delta(dag(u),dag(d)))

Jin

Comments

Thanks for the report, I am seeing the same thing. I'll take a look.

Answer 1

This was indeed a bug in the low level contraction code for contracting block sparse tensors. I've fixed it here: https://github.com/ITensor/NDTensors.jl/pull/64 . The fix will be available in the next ITensors release (v0.1.38), it should be available later today.

Comments

Thanks, Matt.