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technical:ising1d [2022/10/29 14:11] – [Simple case 1: $J = 1$, $h = 0$] chunchungtechnical:ising1d [2022/10/29 15:10] (current) – [Simple case 1: $J = 1$, $h = 0$] chunchung
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 &= Z^{-1} \sum_{\mathbf{s}} E e^{-\beta E} \notag \\ &= Z^{-1} \sum_{\mathbf{s}} E e^{-\beta E} \notag \\
 &= - Z^{-1} \frac{\partial}{\partial\beta} Z \notag \\ &= - Z^{-1} \frac{\partial}{\partial\beta} Z \notag \\
-&= - \frac{\partial}{\partial\beta}\log Z+&= - \frac{\partial}{\partial\beta}\log Z \\ 
 +&= \frac{N\left[\left(e^\beta+e^{-\beta}\right)^{N-1}\left(e^\beta-e^{-\beta}\right)+\left(e^\beta+e^{-\beta}\right)\left(e^\beta-e^{-\beta}\right)^{N-1}\right]}{\left(e^\beta+e^{-\beta}\right)^N+\left(e^\beta-e^{-\beta}\right)^N} \notag \\ 
 +&= N\frac{r+r^{N-1}}{1+r^N}
 \end{align} \end{align}
 +where $r = \left(e^\beta-e^{-\beta}\right)/\left(e^\beta+e^{-\beta}\right)<1$ is the ratio between the two eigenvalues.