Dear ITensor team,

Thanks for your reply and thanks for the wonderful library about TensorNetwork. Recently, I want to calculate spin four point correlation function e.g. <S^{x}*{I}S^{y}*{I+1}S^{x}*{j}S^{y}*{j+1}>.

I am using the latest version of ITensor c++ and i find some documents about how to calculate 2-pt correlation function

I try to coding (just show in the below), but the result is wrong.

op_i = op(sites,“Sx”,i);

auto op_i1 = op(sites,“Sy”,i+1);

op_j = op(sites,“Sx”,j);

auto op_j1 = op(sites,“Sy”,j+1);

//ground state

psi_gs = psi;

psi_gs.position(i);

psi_gsdag = dag(psi_gs);

psi_gsdag.prime(“Link”);

li_1 = leftLinkIndex(psi_gs,i);

auto Cg = prime(psi_gs(i),li_1)*op_i;

Cg *= prime(psi_gsdag(i),“Site”);

Cg *= psi_gs(i+1)*op_i1;

Cg *= prime(psi_gsdag(i+1),“Site”);

for(int k=i+2; k<j;++k)

{

Cg *= psi_gs(k);

Cg *= psi_gsdag(k);

}

Cg *= psi_gs(j)*op_j;

Cg *= prime(psi_gsdag(j),“Site”);

lj = rightLinkIndex(psi_gs,j+1);

Cg *= prime(psi_gs(j+1),lj)*op_j1;

Cg *= prime(psi_gsdag(j+1),“Site”);

auto resultg = eltC(Cg);

Thanks a lot in advance !

Best regards,

Sugar