Creates the model given some input data X and Y.

def _create_model(self, X, Y):
        """
        Creates the model given some input data X and Y.
        """

        # --- define kernel
        self.input_dim = X.shape[1]
        if self.kernel is None:
            kern = GPy.kern.RBF(self.input_dim, variance=1.)
        else:
            kern = self.kernel
            self.kernel = None

        # --- define model
        noise_var = Y.var()*0.01 if self.noise_var is None else self.noise_var
        self.model = GPy.models.GPRegression(X, Y, kernel=kern, noise_var=noise_var)

        # --- Define prior on the hyper-parameters for the kernel (for integrated acquisitions)
        self.model.kern.set_prior(GPy.priors.Gamma.from_EV(2.,4.))
        self.model.likelihood.variance.set_prior(GPy.priors.Gamma.from_EV(2.,4.))

        # --- Restrict variance if exact evaluations of the objective
        if self.exact_feval:
            self.model.Gaussian_noise.constrain_fixed(1e-6, warning=False)
        else:
            self.model.Gaussian_noise.constrain_positive(warning=False)