In this paper we present an integral equation approach for thevaluation of European-style installment derivatives when the paymentplan is assumed to be a continuous function of the asset price andtime. The contribution of this study is threefold. First, we showthat in the Black-Scholes model the option pricing problem can beformulated as a free boundary problem under very general conditionson payoff structure and payment schedule. Second, by applying aFourier transform-based solution technique, we derive a recursiveintegral equation for the free boundary along with an analyticrepresentation of the option price. Third, based on these results,we propose a unified framework which generalizes the existingmethods and is capable of dealing with a wide range of monotonicpayoff functions and continuous payment plans. Finally, by using theillustrative example of European vanilla installment call options,an explicit pricing formula is obtained for time-varying paymentschedules.
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