The dynamical economic model with discrete time and consumer sentiment D. Deac, M. Neamt ¸u and D. Opri¸ s Abstract. The paper describes the Hick Samuelson Keynes dynamical economic model with discrete time and consumer sentiment. We seek to demonstrate that consumer sentiment may create fluctuations in the eco- nomical activities. The model possesses a flip bifurcation and a Neimark- Sacker bifurcation, after which a stable state is replaced by a (quasi-) periodic motion. M.S.C. 2000: 34C23, 37G05, 37G15, 91B42. Key words: consumer sentiment, Hick Samuelson Keynes models, Neimark-Sacker, flip bifurcation, Lyapunov exponent. 1 Introduction The empirical evidence ([2], [10], [4]) suggests that consumer sentiment influ- ences the household expenditure and thus confirms Keynes’suspicion that consumer ”attitudes” and ”animalic spirits” may cause fluctuations in the economic activity. Inspired by these observations, we develop a dynamic economic model in which the agents’consumption expenditures depend on their sentiment. As particular cases, the model contains: the Hick-Samuelson ([9]), Puu ([9]), Keynes ([11]) models, as well as the models from [3] and [11]. The Hick and Solow models have been studied in [1] and [5]. The model possesses a flip and Neimark-Sacker bifurcation, if the autonomous consumption is variable. The paper is organized as follows. In Section 2, we describe the dynamical model with discrete time using the investment, consumption, sentiment and saving functions. For different values of the model parameters we obtain known dynamical models. In Section 3, we analyze the behavior of the dynamical system in the fixed point’s neighborhood for the associated map. We establish asymptotical stability conditions for the flip and Neimark-Sacker bifurcations. In the case of flip and Neimark-Sacker bifurcations, the normal forms are described in Section 4. Using the QR method, the algorithm for the determination of the Lyapunov exponents is presented in Section 5. Finally, the numerical simulation is done. Differential Geometry - Dynamical Systems, Vol.11, 2009, pp. 95-104. c  Balkan Society of Geometers, Geometry Balkan Press 2009.