This paper focuses on modeling the scenario path-dependency of the counterparty credit exposure. The purpose of this paper is threefold: (1) to propose a simple method for consistent estimation of pathwise European swaption exercise probability;(2) to discuss accurate pathwise simulation of barrier option exposure; and (3) to present some exact formulas for the calculation of standalone expected positive exposure and potential future exposure for a single-currency vanilla swap, a physically settled European swaption, and a barrier option without Monte Carlo simulation. These exact formulations are of practical importance to computing standalone exposure profiles, exposure model validation, and system benchmarking.
Keywordspath-dependent exposure, exact exposure profile, swaption exercise probability, barrier survival probability 57 regardless of the number of coupons remaining, follow a single lognormal process. Schmöger (2012) published a detailed calculation based on the approach of Lomibao and Zhu (2006) for both a swaption and a barrier option. Schmöger calculated the swaption exposure only prior to the expiry date because, as he pointed out, "the forward swap rate does not exist after the swaption expiry" (Schmöger, 2012). This means that the forward swap rate for a swap starting at the option expiry ceases to exist past the expiry date, suggesting that the co-terminal swap rates cannot follow a single process.With the DJS, scenarios are generated independently, whereas with the pathwise approach, an entire path is simulated. While the two approaches theoretically generate the same distribution, Ghamami and Zhang (2014) showed that the pathwise approach generates a drastically smaller MSE (mean-squared error) than the DJS. Gregory (2012) also pointed out that a pathwise simulation approach is preferred. In this paper, we demonstrate that the DJS barrier survival probability does not decrease with time.An issue with using a single lognormal swap rate model for swaption exposure in the conditional approach is that a single swap rate model is inconsistent with all the swap rates of the co-terminal swaps spanning the underlying swap, as the number of swap payments decreases with the passage of time. It is clear from the swap rate definition, equation (3.6), that the swap rate depends specifically on the swap term. We show why this is the case and present an alternative approach. This paper has three goals. First, it presents a model for the pathwise probability that a European swaption will be exercised and that the exposure will persist beyond the option expiration date. Our model is based on an Ornstein-Uhlenbeck bridge (OUB) (Corlay, 2014), where the pathwise swaption exercise probability is consistent with the pathwise swap valuation both before and after the option expiry date. Second, it discusses a pathwise approach to the barrier hitting probability. This model takes into account information on the full Monte Carlo path. It demonstrates that the pathwise barrier hitting probability can be significantly d...