Generalization of the correlation function

ITensor C++ Questions
1

Hi everyone,
I am trying to compute the expectation value of a correlation function made up by a string of operators, something like :
C_z=\langle\sigma^1_z\otimes\sigma^2_z\otimes\sigma^3_z\otimes\sigma^4_z\otimes\sigma^5_z\otimes\sigma^6_z\rangle

If you are including code in your question or comment, please put it in a code block as follows:

        int m=1;
        int n=6;
        for(int l = m; l <= n; ++l)
        {
            auto Sz = op(sites,"Sz",l);
            auto C = psi0(l)*Sz;
            auto ir = commonIndex(psi0(l),psi0(l+1),"Link");
            auto D = dag(prime(prime(psi0(l),"Site"),ir));
            if(l==n)
            {   
                auto E=C*D;
                E *=  dag(prime(prime(psi0(l),"Site"),"Link"));
                println("E = ",E);
                elt(E);
            }

        }

I am trying to generalize the following tutorial (ITensor), but I am making some mistake, because E is not a scalar. Any idea on how to fix this ?
Thank you for your time,
Francesco

2

Hi Francesco,

You’re not carrying a (contracted) tensor along for each site, like the C*=... in the tutorial. Ignoring the ends there should be something like

\\set up C tensor here
for(int l = m; l < n; ++l){
  C*= psi0(l)*op(sites,"Sz",l);
  C*= dag(prime(psi0(l));
}

within the loop

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3

Thank you for your answer, now I figured it out and it is working properly !

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