ABSTRACT
The LIBOR Market Model has become one of the most popular models for pricing interest rate products. It is commonly believed that Monte-Carlo simulation is the only viable method available for the LIBOR Market Model. In this article, however, we propose a lattice approach to price interest rate products within the LIBOR Market Model by introducing a shifted forward measure and several novel fast drift approximation methods. This model should achieve the best performance without losing much accuracy. Moreover, the calibration is almost automatic and it is simple and easy to implement. Adding this model to the valuation toolkit is actually quite useful; especially for risk management or in the case there is a need for a quick turnaround.
Key Words : LIBOR Market Model, lattice model, tree model, shifted forward measure, drift approximation, risk management, calibration, callable exotics, callable bond, callable capped floater swap, callable inverse floater swap, callable range accrual swap.
an interest rate model based on evolving LIBOR market forward rates under a risk-neutral forward probability measure. In contrast to models that evolve the instantaneous short rates (e.g., Hull-White, Black-Karasinski models) or instantaneous forward rates (e.g., Heath-Jarrow-Morton (HJM) model), which are not directly observable in the market, the objects modeled using the LMM are market observable quantities. The explicit modeling of market forward rates allows for a natural formula for interest rate option volatility that is consistent with the market practice of using the formula of Black for caps. It is generally considered to have more desirable theoretical calibration properties than short rate or instantaneous forward rate models.
In general, it is believed that simulation is the only viable numerical method available for the LMM (see Piterbarg [2003]). The simulation is computationally expensive, slowly converging, and notoriously difficult to use for calculating sensitivities and hedges. Another notable weakness is its inability to determine how far the solution is from optimality in any given problem.
In this paper, we propose a lattice approach within the LMM. The model has similar accuracy to the current pricing models in the market, but is much faster. Some other merits of the model are that calibration is almost automatic and the approach is less complex and easier to implement than other current approaches.
We introduce a shifted forward measure that uses a variable substitution to shift the center of a forward rate distribution to zero. This ensures that the distribution is symmetric and can be represented by a relatively small number of discrete points. The shift transformation is the key to achieve high accuracy in relatively few discrete finite nodes. In addition, we present several fast and novel drift approximation approaches. Other concepts used in the model are probability distribution structure exploitation, numerical integration and the long jump technique (we only position nodes at times when decisions need to be made).
This model is actually quite useful for risk management because normally full-revaluations of an entire portfolio under hundreds of thousands of different future scenarios are required for a short time window (see FinPricing (2011)). Without an efficient algorithm, one cannot properly capture and manage the risk exposed by the portfolio.
The rest of this paper is organized as follows: The LMM is discussed in Section I. In Section II, the lattice model is elaborated. The calibration is presented in Section III. The numerical implementation is detailed in Section IV, which will enhance the reader’s understanding of the model and its practical implementation. The conclusions are provided in Section V.
  1. LIBOR MARKET MODEL
Let (,,,) be a filtered probability space satisfying the usual conditions, where denotes a sample space, denotes a -algebra, denotes a probability measure, and denotes a filtration. Consider an increasing maturity structure from which expiry-maturity pairs of dates (,) for a family of spanning forward rates are taken. For any time , we define a right-continuous mapping function by . The simply compounded forward rate reset at t for forward period (,) is defined by
(1)
where denotes the time t price of a zero-coupon bond maturing at time T and is the accrual factor or day count fraction for period (,).
Inverting this relationship (1), we can express a zero coupon bond price in terms of forward rates as:
(2)