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With regard to importance of investment as an engine of economic growth many economists such as Wicksel, Keynse and Harrod believe that investment is the main source of business cycles. Hence this study specifies investment function according to a basic macroeconomic model such as Ramsey model. Application of Ramsey model can help to extend macroeconomics with micro foundations in economy of Iran and prepares new scopes for researchers. The main idea of this study is specification of investment function according to Ramsey model and its estimation by cointegration technique for period (1990:Q1-2007:Q4). The result of econometric estimation indicated a long run relationship between investment, capital stock, and shadow price of capital, installation cost of capital, capital price and terms of trade. Results showed that capital stock, shadow price of capital and terms of trade have direct effects and, installation cost of capital and capital price have inverse effect on investment.

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This paper aims to determine the optimum price of electricity during restructuring process. We maximized social welfare function subject to market equilibrium, maximum production capacity of each group of power plants, maximum demand of each consumer type and the potential of electricity export and import. The model was run using 2007 monthly and annual data by means of GAMS optimization software. The calculated electricity shadow price for the year 2007 was 371.2 per KWh. To get more exact results we run the model for each month separately. The results show that the price of electricity in spring and summer is lower than fall and winter, for marginal cost of power provision in winter rises. This is due to substitution of gas by gasoil and other liquid fuels and also reduction of hydropower production. For both intervals the actual price has a significant deviation from optimum price in Iranian power market.