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--- exercise:prog:spinglass [2020/08/13 08:28] – created chunchung
+++ exercise:prog:spinglass [2020/11/06 03:15] (current) – [System representation] chunchung
@@ Line 1: / Line 1: @@
 ======Programming: Monte-Carlo simulation of spin-glass model======
+Write a complete Monte-Carlo simulation program for the [[https://en.wikipedia.org/wiki/Spin_glass#The_model_of_Sherrington_and_Kirkpatrick|Sherrington–Kirkpatrick model]] of spin glass.
+The model is defined by the Hamiltonian,
+\[H=-\sum_{i<j}J_{i,j}s_i s_j,\]
+where $s_i=\pm 1$ with $i=0,..,N-1$ are the $N$ spins of the system.
+=====System representation=====
+Both structure ($h_i$,$J_{i,j}$) and state ($s_i$) data are stored in one dimensional arrays.
+<code c++>
+int sz = 64;
+int * spin = new int[sz];
+double * h = new double [sz];
+double * j = new double [sz*(sz-1)/2];
+</code>
+Since the coupling involves two spins, it is instinctive to use a two-dimensional array for ''j''. However, in a more general view, it is clearer to serialize the iteration into one over links instead of two nodes. This also reduces redundancy.
+Since we are using %%C++%%, we will use the ''vector'' class in place of array pointers:
+<code c++>
+std::vector<int> spin;
+std::vector<double> h;
+std::vector<double> j;
+</code>
+For couplings, we use ''struct Link'' to keep track of the nodes involved in each bond.
+<code c++>
+struct Link {
+	int n0;
+	int n1;
+};
+std::vector<Link> lnks;
+</code>
+=====Data storage=====
+For portability of data, we use [[https://www.hdfgroup.org/solutions/hdf5/|HDF5]] library. Here, we try the C++ binding of the library.
+<code c++>
+#include <H5Cpp.h>
+#include <vector>
+std::vector<double> h;
+std::vector<double> j;
+void load_params(std::string filename)
+{
+        using namespace H5;
+        H5File f(filename,H5F_ACC_RDONLY);
+        // read h
+        DataSet d = f.openDataSet("h");
+        hsize_t sz;
+        d.getSpace().getSimpleExtentDims(&sz,0);
+        h.resize(sz);
+        d.read(h.data(),PredType::NATIVE_DOUBLE);
+        // read j
+        d = f.openDataSet("j");
+        d.getSpace().getSimpleExtentDims(&sz,0);
+        j.resize(sz);
+        d.read(j.data(),PredType::NATIVE_DOUBLE);
+}
+</code>
+=====All-to-all network=====

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