Abstract

This research work investigates the theoretical foundations and computational aspects of constructing optimal bespoke CDO structures. Due to the evolutionary nature of the CDO design process, stochastic search methods that mimic the metaphor of natural biological evolution are applied. For efficient searching the optimal solution, the nondominating sort genetic algorithm (NSGA-II) is used, which places emphasis on moving towards the true Paretooptimal region. This is an essential part of real-world credit structuring problems. The algorithm further demonstrates attractive constraint handling features among others, which is suitable for successfully solving the constrained portfolio optimisation problem. Numerical analysis is conducted on a bespoke CDO collateral portfolio constructed from constituents of the iTraxx Europe IG S5 CDS index. For comparative purposes, the default dependence structure is modelled via Gaussian and Clayton copula assumptions. This research concludes that CDO tranche returns at all levels of risk under the Clayton copula assumption performed better than the sub-optimal Gaussian assumption. It is evident that our research has provided meaningful guidance to CDO traders, for seeking significant improvement of returns over standardised CDOs tranches of similar rating.

Highlights

  • Bespoke CDOs provides tailored credit solutions to market participants

  • Understanding the risk/return trade-off dynamics underlying the bespoke CDO collateral portfolios is crucial when maximising the utility provided by these instruments

  • The single-tranche deal can be put together in a relatively short period of time. This is aided by the development of numerous advance pricing, risk management and portfolio optimisation techniques

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Summary

Introduction

Bespoke CDOs provides tailored credit solutions to market participants. They provide both long-term strategic and tactical investors with the ability to capitalise on views at the market, sector and name levels. Investors often express preferences on individual names, and there is likely to be credit rating constraint and industry concentration limits imposed by the investors and rating agencies 2 Given these various investor defined requirements, the structurer is required to optimise the portfolio to achieve the best possible tranche spreads for investors. The main features of these algorithms are the implementation of a fast nondominated sorting procedure and its ability to handle constraints without the use of penalty functions The latter feature is essential for solving the multiobjective CDO optimisation problem. A robust and practical CDO valuation framework based on the application of the single-factor copula models given, is presented This is in conjunction with weighted Monte Carlo techniques used in options pricing. The final section highlights the improtant research findings and discusses several areas of future study

Bespoke CDO Mechanics
Credit Selection for the Reference portfolio
Defining the Subordination Level and Tranche Size
Substitution of Credits in the Reference portfolio
Factor Copula Models for Default Dependence Modelling
Gaussian Copula
Clayton Coupla
Implied Factor Copula Models for CDO Valuation
Synthetic CDO Pricing
E PVpnrotrt
Weighted Monte Carlo Techniques
Mathematical Formulation
Objective Functions
Constraint Description
Augmented Lagrangian Methods
Implementation Issues
Interpreting the Implied Distributions
Risk Characterisation of Credit portfolios
Optimal Bespoke CDO Design
Multiobjective Optimisation
Representation of Individuals
Evaluation Function
Population Models and Diversity Preservation
Crowded Comparison Operator
Nondomination Sorting Approach
Parent Selection Mechanism
Mutation Operation
Recombination Operation
Main Loop
6.2.10. Initialisation and Termination Conditions
E Lntr tj
Optimal Structures with Long Only Credit portfolio
Issuer Concentrated Credit Structures
Conclusions
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