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Mixed Integer Programming Approaches for Index Tracking and Enhanced Indexation. Nilgun Canakgoz, John Beasley. Department of Mathematical Sciences, Brunel University CARISMA: Centre for the Analysis of Risk and Optimisation Modelling Applications. Outline. Introduction Problem formulation
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Mixed Integer Programming Approaches for Index Tracking and Enhanced Indexation Nilgun Canakgoz, John Beasley Department of Mathematical Sciences, Brunel University CARISMA: Centre for the Analysis of Risk and Optimisation Modelling Applications
Outline • Introduction • Problem formulation • Index Tracking • Enhanced Indexation • Computational results • Conclusion
Introduction • Passive fund management • Index tracking • Full replication • Fewer stocks • Tracking portfolio (TP)
Problem Formulation • Notation • N : number of stocks • K : number of stocks in the TP • εi : min proportion of TP held in stock i • δi : max proportion of TP held in stock i • Xi : number of units of stock i in the current TP • Vit : value of one unit of stock i at time t • It : value of index at time t • Rt : single period cont. return given by index
Problem Formulation • C : total value of TP • :be the fractional cost of selling one unit of stock i at time T • :be the fractional cost of buying one unit of stock i at time T • : limit on the proportion of C consumed by TC • xi : number of units of stock i in the new TP • Gi : TC incurred in selling/buying stock i • zi = 1 if any stock i is held in the new TP = 0 otherwise • rt : single period cont. return by the new TP
Problem Formulation • Constraints • (1) • (2) • (3) • (4)
Problem Formulation • (5) • (6) • (7) • (8)
Problem Formulation • Index Tracking Objective • Single period continuous time return for the TP (in period t) is a nonlinear function of the decision variables • To linearise, we shall assume • Linear weighted sum of individual returns • Weights summing to 1
Problem Formulation • Hence the return on the TP at time t • Approximate Wit by a constant term which is independent of time • Hence the return on the TP at time t
Problem Formulation • Our expression for wi is nonlinear, to linearise it we first use equation (6) and then equation (5) to get (9) • Finally we have a linear expression (approximation) for the return of the TP • If we regress these TP returns against the index returns (10), (11)
Problem Formulation • Ideally, we would like, for index-tracking, to choose K stocks and their quantities (xi) such that we achieve • We adopt the single weighted objective , user defined weights
Problem Formulation • The modulus objective is nonlinear and can be linearised in a standard way (13) (14) (15) (16) (17)
Problem Formulation • Our full MIP formulation for solving index-tracking problem is subject to (1)-(11) and (13)-(17) • This formulation has 3N+4 continuous variables, N zero-one variables and 4N+9 constraints
Problem Formulation • Two-stage approach • Let and be numeric values for and when we use our formulation above • Then the second stage is (19) subject to (1)-(11) and (13)-(17) and (20) (21)
Problem Formulation • Enhanced indexation • One-stage approach to enhanced indexation is: subject to (1)-(11),(13)-(17) and
Problem Formulation • Two-stage approach is precisely the same as seen before, namely minimise (19) subject to (1)-(11), (13)-(17), (20), (21)
Computational Results • Data sets • Hang Seng, DAX, FTSE, S&P 100, Nikkei, S&P 500, Russell 2000 and Russell 3000 • Weekly closing prices between March 1992 and September 1997 (T=291) • Model coded in C++ and solved by the solver Cplex 9.0 (Intel Pentium 4, 3.00Ghz, 4GB RAM)
Computational Results • The initial TP composed of the first K stocks in equal proportions, i.e.
Index Tracking In-Sample vs. Out-of-Sample Results
Systematic Revision • To investigate the performance of our approach over time we systematically revise our TP • Set T=150 • Use our two-stage approach to decide the new TP [xi] • Set [Xi]=[xi] (replace the current TP by the new TP) • Set T=T+20 and if T 270 go to (b)
Enhanced Indexation In-Sample vs. Out-of-Sample Results
Conclusion • Good computational results • Reasonable computational times in all cases