First draft of Ising model

include/IsingModel.hpp

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+/** @file IsingModel.hpp
+ *
+ *  @author Cory Alexander Balaton (coryab)
+ *  @author Janita Ovidie Sandtrøen Willumsen (janitaws)
+ *
+ *  @version 0.1
+ *
+ *  @brief The definition of the Ising model.
+ *
+ *  @bug No known bugs
+ * */
+#ifndef __ISING_MODEL__
+#define __ISING_MODEL__
+
+#include "typedefs.hpp"
+
+#include <armadillo>
+#include <random>
+#include <unordered_map>
+
+// Faster modulo
+#define INDEX(I, N) (I + N) % N
+
+// Indeces for the neighbor matrix.
+#define UP 0
+#define LEFT 0
+#define DOWN 1
+#define RIGHT 1
+
+/** @brief The Ising model in 2 dimensions.
+ *
+ *  @details Here we set \f$ J = 1 \f$, and the Boltzmann constant
+ *  \f$ k_B = 1 \f$.
+ * */
+class IsingModel {
+private:
+    friend class IsingModelTest;
+    /** @brief \f$ L \cross L \f$ matrix where element $ x \in {-1, 1}$.
+     * */
+    arma::Mat<int> lattice;
+
+    arma::Mat<uint> neighbors;
+
+    /** @brief A hash map containing all possible energy changes.
+     * */
+    std::unordered_map<int, double> energy_diff;
+
+    /** @brief Temperature
+     * */
+    double T;
+
+    uint L;
+
+    /** @brief The current energy state. unit: \f$ J \f$.
+     * */
+    int E;
+
+    /** @brief The current magnetic strength. unit: Unitless.
+     * */
+    int M;
+
+    /** @brief Energy per spin. unit: \f$ J \f$.
+     * */
+    double eps;
+
+    /** @brief Magnetization per spin. unit: Unitless.
+     * */
+    double m;
+
+    /** @brief Initialize the lattice with a random distribution of 1s and
+     *  -1s.
+     * */
+    void initialize_lattice();
+
+    void initialize_neighbors();
+
+    /** @brief Initialize the hashmap with the correct values.
+     * */
+    void initialize_energy_diff();
+
+    /** @brief Initialize the model.
+     * */
+    void initialize_magnetization();
+
+    void initialize_energy();
+
+public:
+    /** @brief Constructor for the Ising model.
+     *
+     *  @param L The size of the lattice.
+     * */
+    IsingModel(uint L, double T);
+
+    /** @brief Constructor for the Ising model.
+     *
+     *  @param L The size of the lattice.
+     * */
+    IsingModel(uint L, double T, int val);
+
+    void Metropolis(std::mt19937 engine);
+};
+
+#endif