Given the agent's desired novelty, how good the novelty value is.

        Not used if *desired_novelty*=-1

def hedonic_value(self, novelty):
        '''Given the agent's desired novelty, how good the novelty value is.

        Not used if *desired_novelty*=-1
        '''
        lmax = gaus_pdf(self.desired_novelty, self.desired_novelty, 4)
        pdf = gaus_pdf(novelty, self.desired_novelty, 4)
        return pdf / lmax