Infinite error during CTMRG.

[Gertian]

I'm trying to to run PEPSKit for the pi-flux model (which lives on a 2 by 2 unit cell with fermions) and I'm bumping into some issues. More specifically leading_boundary(CTMRGEnv(state, χ), state, ctm_alg); gives me an infinite error for all except the first iteration.

A MWE ( which doesn't even care about the Hamiltonian yet) is :

using Revise
using TensorKit, PEPSKit, KrylovKit, OptimKit
########################################
#Define the symmetry gorup of the model#
########################################
sym = (SU2Irrep ⊠ U1Irrep ⊠ FermionParity);  #mixing colors * PN_conservation * it's fermions
#define some elementary IRREPS of this symmetry group.
empty  = sym.(0   ,0,0);  #empty empty
single = sym.(1//2,1,1);  #full empty + empty full
double = sym.(0   ,2,0);  #full full
#define the physical Hilbert space of this model :
ph = Vect[sym](empty => 1, single => 1, double => 1);

#############
#Find the GS#
#############
#define IC
D = Vect[sym](empty => 1, single=>1, double=>1)  #intial space of PEPS
intitial_tensors = [TensorMap(rand, ComplexF64, ph, D*D'*D'*D)  TensorMap(rand, ComplexF64, ph, D*D'*D'*D) ;
                    TensorMap(rand, ComplexF64, ph, D*D'*D'*D)  TensorMap(rand, ComplexF64, ph, D*D'*D'*D) ]  ;
initial_state = InfinitePEPS(intitial_tensors);

#Define the GS_search algorithm 
χ = Vect[sym](empty => 3, single=>3, double=>3)  #intial space of the boundary MPS
χ_max = 20                                       #maximal bond dimension of the boundary MPS
ctm_alg = CTMRG(; tol=1e-10, miniter=4, maxiter=100, verbosity=3, trscheme=truncdim( χ_max )); #verbosity can be lowered if you want less output.

#use the above to actually get the GS
state = initial_state
environments = leading_boundary(CTMRGEnv(state, χ), state, ctm_alg);  #initial boundaries

I also ran the same code with sym = (SU2Irrep ⊠ U1Irrep ⊠ Z2Irrep) which produces the same error. Therefore I suspect the issue doesn't sit with the fermionic reps.

[lkdvos]

can you also attach the error? what is an infinite error?

[Gertian]

I mean literally "an infinite error" .

[lkdvos]

that's not unexpected behavior, that means that the virtual spaces are still changing, in which case the difference between two iterations is not very well defined, and it returns Inf

[Gertian]

Ok I see, thanks !