= Sherrington-Kirkpatrick model
{c}
{title2=$J_{ij}=J_0/N+\mathcal J z_{ij}/\sqrt N$}
The <Sherrington-Kirkpatrick model> couples every distinct pair of <Ising spins> using independent standard <normal random variables> $z_{ij}$ for $i<j$, with $J_{ji}=J_{ij}$. Here $J_0$ and $\mathcal J$ have units of <energy>. <David Sherrington> and <Scott Kirkpatrick> introduced this scaling in 1975; their original replica-symmetric calculation gave an unphysical negative low-temperature <entropy>. The model and that initial proposed solution must be distinguished.<Solvable Model of a Spin-Glass by David Sherrington and Scott Kirkpatrick>[pp. 1793 and 1795, coupling scaling (2), replica-symmetric assumption and acknowledged negative entropy]{ref}
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