Make changes

include/IsingModel.hpp

@@ -18,6 +18,7 @@
 #include "utils.hpp"
 
 #include <armadillo>
+#include <cstdint>
 #include <random>
 #include <unordered_map>
 
@@ -53,7 +54,8 @@ private:
 
     /** @brief A hash map containing all possible energy changes.
      * */
-    std::unordered_map<int, double> energy_diff;
+    //std::unordered_map<int, double> energy_diff;
+    double energy_diff[17];
 
     /** @brief The temperature of the model.
      * */
@@ -65,12 +67,15 @@ private:
 
     /** @brief The current energy state. unit: \f$ J \f$.
      * */
-    int E;
+    int64_t E;
 
     /** @brief The current magnetic strength. unit: Unitless.
      * */
-    int M;
+    int64_t M;
 
+    std::mt19937 engine;
+
+    void initialize_engine();
     /** @brief Initialize the lattice with a random distribution of 1s and
      *  -1s.
      * */