Plots the model and the acquisition function.
            if self.input_dim = 1: Plots data, mean and variance in one plot and the acquisition function in another plot
            if self.input_dim = 2: as before but it separates the mean and variance of the model in two different plots
        :param filename: name of the file where the plot is saved

def plot_acquisition(self,filename=None):
        """
        Plots the model and the acquisition function.
            if self.input_dim = 1: Plots data, mean and variance in one plot and the acquisition function in another plot
            if self.input_dim = 2: as before but it separates the mean and variance of the model in two different plots
        :param filename: name of the file where the plot is saved
        """
        if self.model.model is None:
            from copy import deepcopy
            model_to_plot = deepcopy(self.model)
            if self.normalize_Y:
                Y = normalize(self.Y, self.normalization_type)
            else:
                Y = self.Y
            model_to_plot.updateModel(self.X, Y, self.X, Y)
        else:
            model_to_plot = self.model

        return plot_acquisition(self.acquisition.space.get_bounds(),
                                model_to_plot.model.X.shape[1],
                                model_to_plot.model,
                                model_to_plot.model.X,
                                model_to_plot.model.Y,
                                self.acquisition.acquisition_function,
                                self.suggest_next_locations(),
                                filename)