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Update 2016-11-03-ocihd.md #3

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28 changes: 14 additions & 14 deletions _posts/2016-11-03-ocihd.md
Original file line number Diff line number Diff line change
Expand Up @@ -42,29 +42,29 @@ The general idea is to solve
$$\hat{s}=\text{argmin}(\sum_{N}\rho(\varepsilon_{\mu})+\sum_{P}\sigma(s_{i}))$$

for generic convex $$\rho$$ an $$\sigma$$ by:
1. Defining a physical system augmented with an inverse temperature
$$\beta$$ whose ground state is a solution to the problem as $$\beta\rightarrow\infty$$.
The energy in terms of $$u=s^{0}-s$$ is:
1. Defining a physical system augmented with an inverse temperature
$$\beta$$ whose ground state is a solution to the problem as $$\beta\rightarrow\infty$$.
The energy in terms of $$u=s^{0}-s$$ is:

$$E(u)=\sum_{N}\rho(\varepsilon_{\mu}+X_{\mu j}u_{j})+\sum_{P}\sigma(s_{j}^{0}-u_{j})$$

2. Calculating the free energy of the system using the replica trick
A physical system in the micro-canonical ensemble minimizes $$E$$. A physical system in the canonical ensemble (held at constant temperature $$\frac{1}{\beta}$$) minimizes the free energy
2. Calculating the free energy of the system using the replica trick
A physical system in the micro-canonical ensemble minimizes $$E$$. A physical system in the canonical ensemble (held at constant temperature $$\frac{1}{\beta}$$) minimizes the free energy

$$F=E-TS=\left\langle -\log(Z)\right\rangle =\left\langle -\log(\int \mathrm{d}u e^{-\beta E(u)})\right\rangle.$$
$$F=E-TS=\left\langle -\log(Z)\right\rangle =\left\langle -\log(\int \mathrm{d}u e^{-\beta E(u)})\right\rangle.$$

3. Taking the $$\beta\rightarrow\infty$$ limit.
3. Taking the $$\beta\rightarrow\infty$$ limit.

The general idea of the replica trick is to calculate an average over a polynomial of $$Z$$
instead of an intractable function of $$Z$$. The free energy is calculated using:
The general idea of the replica trick is to calculate an average over a polynomial of $$Z$$
instead of an intractable function of $$Z$$. The free energy is calculated using:

$$
F=-\left\langle \log Z\right\rangle = \lim_{n\rightarrow 0}\left\langle \frac{Z^{n}-1}{n}\right\rangle =\lim_{n\rightarrow 0} \left\langle \frac{\partial Z^{n}}{\partial n}\right\rangle
$$
$$
F=-\left\langle \log Z\right\rangle = \lim_{n\rightarrow 0}\left\langle \frac{Z^{n}-1}{n}\right\rangle =\lim_{n\rightarrow 0} \left\langle \frac{\partial Z^{n}}{\partial n}\right\rangle
$$

Where $$Z^{n}$$ is the partition function of n "copies" of the system. The integral over $$X$$, $$s^{0}$$ and $$\varepsilon$$ couples these copies. This interpretation is valid for integer $$n$$, but the formula is taken to hold for continuous $$n$$
Where $$Z^{n}$$ is the partition function of n "copies" of the system. The integral over $$X$$, $$s^{0}$$ and $$\varepsilon$$ couples these copies. This interpretation is valid for integer $$n$$, but the formula is taken to hold for continuous $$n$$

We get:
We get:

$$
\left\langle Z^{n}\right\rangle = \left\langle \int \prod_{a=1}^{n} \mathrm{d}u^{a} e^{-\sum_a \beta E(u^{a})} \right\rangle
Expand Down