builder
.registerTypeAdapter(ModelHolder.class, new JsonModelHolderAdapter());
Gson gson = builder.create();
double[] d = {1.1, 2.2};
double[] s = {3.3, 4.4};
ModelHolder mh = new ModelHolder(new AsymmetricSampledNormalModel(
new DenseVector(d), new DenseVector(s)));
String format = gson.toJson(mh);
System.out.println(format);
ModelHolder mh2 = gson.fromJson(format, ModelHolder.class);
assertEquals("mh", mh.getModel().toString(), mh2.getModel().toString());