Add to method and conclusion.

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# Ising model related literature
@misc{hj:2015:comp_phys,
author = {Morten Hjorth-Jensen},
howpublished = {\url{https://raw.githubusercontent.com/CompPhysics/ComputationalPhysics/master/doc/Lectures/lectures2015.pdf}},
title = {Computational Physics, Lecture Notes Fall 2015},
year = {2015}
}
@misc{britannica:2023:ferromagnetism,
author = {Britannica, The Editors of Encyclopaedia},
title = {ferromagnetism},

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\begin{document}
\section{Conclusion}\label{sec:conclusion}
% Draft based on abstract
We have used the Ising model to study the behavior in ferromagnets, when undergoing
a phase transition near a critical temperature. We generated samples using the
Markov chain Monte Carlo method, while utilizing methods of parallelization.
Finding the burn-in time to be approx. 3000 Monte Carlo cycles. For temperature
$T = 1.0 J / k_{B}$ we found a propability distrobution with an expected mean
value of $\mu \approx -1.9969$ and variation $\sigma^{2} = 0.0001$. Whereas the
pdf close to the critical temperature is $\mu \approx -1.2370$ and variation
$\sigma^{2} = 0.0203$. We estimated the expected energy and magnetization per spin,
in addition to the heat capacity and susceptibility. Using the values from
finite sized lattices, we approximated the critical temperature of an infinite
sized lattice. Using linear regression, we numerically estimated $T_{c}$ $T_{C}(L = \infty) \approx 2.2695$
which is close to the analytical solution $T_{C}(L = \infty) \approx 2.269 J/k_{B}$
found by Lars Onsager.
\end{document}

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@ -80,7 +80,8 @@ have two spins oriented up the total energy have two possible values, as shown i
conditions.}
\label{tab:lattice_config}
\end{table}
We use the analytical values, found in Table for both for lattices where $L = 2$ and $L > 2$.
We use the analytical values, found in Table for both for lattices where $L = 2$
and $L > 2$.
However, to compare the quantities for lattices where $L > 2$, we find energy
per spin given by
@ -94,6 +95,7 @@ and magnetization per spin given by
\label{eq:magnetization_spin}
\end{equation}
\subsection{Statistical mechanics}\label{subsec:statistical_mechanics}
When we study ferromagnetism, we have to consider the probability for a microstate
$\mathbf{s}$ at a fixed temperature $T$. The probability distribution function
@ -103,13 +105,19 @@ $\mathbf{s}$ at a fixed temperature $T$. The probability distribution function
\label{eq:boltzmann_distribution}
\end{equation}
known as the Boltzmann distribution. This is an exponential distribution, where
$\beta$ and $Z$ are given by
\begin{align*}
\beta =& \frac{1}{k_{B}} \ , &
Z &= \sum_{\text{all possible } \mathbf{s}} e^{-\beta E(\mathbf{s})} \ , \\
\end{align*}
and $k_{B}$ is the Boltzmann constant. $Z$ is a normalizing factor of the pdf,
known as the partition function, which we derive in Appendix \ref{sec:partition_function}
$\beta$ is given by
\begin{equation}
\beta = \frac{1}{k_{B}} \ ,
\label{eq:beta}
\end{equation}
where and $k_{B}$ is the Boltzmann constant. $Z$ is a normalizing factor of the
pdf, given by
\begin{equation}
Z = \sum_{\text{all possible } \mathbf{s}} e^{-\beta E(\mathbf{s})} \ ,
\label{eq:partition}
\end{equation}
and is known as the partition function. We derive $Z$ in Appendix \ref{sec:partition_function},
which gives us
\begin{equation*}
Z = 4 \cosh (8 \beta J) + 12 \ .
\end{equation*}
@ -117,27 +125,28 @@ Using the partition function and Eq. \eqref{eq:boltzmann_distribution}, the pdf
of a microstate at a fixed temperature is given by
\begin{equation}
p(\mathbf{s} \ | \ T) = \frac{1}{4 \cosh (8 \beta J) + 12} e^{-\beta E(\mathbf{s})} \ .
\label{eq:pdf}
\end{equation}
% Add something about why we use the expectation values?
We derive the analytical expressions for expectation values in Appendix.
\ref{sec:expectation_values}. We find the expected total energy
\begin{equation*} %\label{eq:energy_total_first}
\begin{equation}\label{eq:energy_total_result}
\langle E \rangle = -\frac{8J \sinh(8 \beta J)}{\cosh(8 \beta J) + 3} \ ,
\end{equation*}
\end{equation}
and the expected energy per spin
\begin{equation*} %\label{eq:energy_spin_first}
\begin{equation}\label{eq:energy_spin_result}
\langle \epsilon \rangle = \frac{-2J \sinh(8 \beta J)}{ \cosh(8 \beta J) + 3} \ .
\end{equation*}
\end{equation}
We find the expected absolute total magnetization
\begin{equation*} %\label{eq:magnetization_total_first}
\begin{equation}\label{eq:magnetization_total_result}
\langle |M| \rangle = \frac{2(e^{8 \beta J} + 2)}{\cosh(8 \beta J) + 3} \ ,
\end{equation*}
\end{equation}
and the expected magnetization per spin
\begin{equation*} %\label{eq:magnetization_spin_first}
\begin{equation}\label{eq:magnetization_spin_result}
\langle |m| \rangle = \frac{e^{8 \beta J} + 1}{2( \cosh(8 \beta J) + 3)} \ .
\end{equation*}
\end{equation}
We will also determine the heat capacity
We also need to determine the heat capacity
\begin{equation}
C_{V} = \frac{1}{k_{B} T^{2}} (\mathbb{E}(E^{2}) - [\mathbb{E}(E)]^{2}) \ ,
\label{eq:heat_capacity}
@ -180,6 +189,12 @@ Boltzmann constant we derive the remaining units, which can be found in Table
\subsection{Phase transition and critical temperature}\label{subsec:phase_critical}
% P9 critical temperature
When a ferromagnetic material is heated, it will change at a macroscopic level.
Based on a $2 \times 2$ lattice, we can show that the total energy is equal to the
energy where all spins have the orientation up \cite[p. 426]{hj:2015:comp_phys}.
Increasing the temperature of the external field, the Ising model move from an
ordered to an unordered phase. At the critical temperature the heat capacity $C_{V}$,
and the magnetic susceptibility $\chi$ diverge \cite[p. 431]{hj:2015:comp_phys}.
\subsection{The Markov chain Monte Carlo method}\label{subsec:mcmc_method}
Markov chains consist of a sequence of samples, where the probability of the next