Asset valuation and optimal investment

Transcription

1 Asset valuation and optimal investment Teemu Pennanen Department of Mathematics King s College London 1 / 57

2 Optimal investment and asset pricing are often treated as separate problems (Markovitz vs. Black Scholes). In practice, valuations have been largely disconnected from investment and risk management. This lead to large losses during 2008 e.g. with credit derivatives. Building on convex stochastic optimization, we describe a unified approach to optimal investment, valuation and risk management. The resulting valuations are based on hedging costs, extend and unify financial and actuarial valuations, reduce to risk neutral valuations for replicable securities. 2 / 57

3 Pennanen, Optimal investment and contingent claim valuation in illiquid markets, Finance and Stochastics, Armstrong, Pennanen, Rakwongwan, Pricing and hedging of S&P500 options under illiquidity, manuscript. King, Koivu, Pennanen, Calibrated option bounds, Int. J. Theor. Appl. Finance, Nogueiras, Pennanen, Pricing and hedging EONIA swaps under illiquidity and credit risk, manuscript. Hilli, Koivu, Pennanen, Cash-flow based valuation of pension liabilities. European Actuarial Journal, Bonatto, Pennanen, Optimal hedging and valuation of oil refineries and supply contracts, manuscript. Pennanen, Perkkiö, Convex duality in optimal investment and contingent claim valuation in illiquid markets, manuscript. 3 / 57

4 Asset-Liability Management Let M be the linear space of adapted sequences of cash-flows on a filtered probability space (Ω,F,(F t ) T t=0,p). The financial market is described by a convex set C M of claims that can be superhedged without cost (i.e. each c C is freely available in the financial market). In models with a perfectly liquid cash-account, T C = {c M c t C} t=0 where C L 0 (Ω,F T,P) are the claims at T that can be hedged without cost [Delbaen and Schachermayer, 2006]. Conical C: [Dermody and Rockafellar, 1991], [Jaschke and Küchler, 2001], [Jouini and Napp, 2001], [Madan, 2014]. 4 / 57

5 Asset-Liability Management Example 1 (The classical model) In the classical perfectly liquid market model with a cash-account C = {c M x N : T c t T 1 x t s t+1 } t=0 t=0 which is a convex cone. This set has been extensively studied in the literature; see e.g. [Föllmer and Schied, 2004] or [Delbaen and Schachermayer, 2006] and their references. 5 / 57

6 Asset-Liability Management The limit order book of TDC A/S in Copenhagen Stock Exchange on January 12, 2005 at 13:58: PRICE QUANTITY 6 / 57

7 Asset-Liability Management Consider an agent with liabilities c M, access to C and a loss function V : M R that measures disutility/regret/ risk/...of delivering c M. For example, V(c) = E T t=0 u t ( c t ). The agent s problem can be written as ϕ(c) = inf d C V(c d) We assume that V is convex and nondecreasing with V(0) = 0. 7 / 57

8 Example: Oil derivatives We study the problem of a derivatives trader who aims to optimize his end of the year derivatives book P/L. The market consists of 12 futures contracts with 12 maturities on five oil products: Brent: North Sea Brent Crude, WTI: West Texas Intermediate Crude Oil, RBOB: Reformulated Gasoline Blendstock, HO: NY Harbor Ultra Low Sulphur Diesel, Gasoil: Low Sulphur Gasoil. This is joint work with Luciane Bonatto, Petrobras. 8 / 57

9 Example: Oil derivatives 9 / 57

10 Example: Oil derivatives Denote the spot price of underlying i at time t by S t,i. The payouts of long and short positions in a futures contract with maturity t are given by c l t = S t,i F a t, c s t = F b t S t,i for outright contracts and c l t = (S t,i S t,j ) F a t c s t = F b t (S t,i S t,j ) for spread contracts. Here F b t,f a t are the bid and ask futures prices. Both bid and ask prices come with finite quantities q a,q b 10 / 57

11 Example: Oil derivatives Figure 1: Market bid and ask futures prices and volume 11 / 57

12 Example: Oil derivatives 12 / 57

13 Example: Oil derivatives 13 / 57

14 Example: Oil derivatives 14 / 57

15 Example: Oil derivatives 15 / 57

16 Example: Oil derivatives 16 / 57

17 Example: Oil derivatives The set of superhedgeable claims becomes C = {c M w M, x (R 2K + ) 12 : c t +w t r t w t 1 + k K (x l,k t c l,k t +x s,k t c s,k t )} where K is the set of traded contracts and w t monthly cash position with w 1 := 0, r t monthly return on cash, c k,l t,c k,s t net cash-flows of long/short position in the kth forward, x l,k t,x s,k t long/short position in the kth swap (to be optimized), c t agent s cash-flows to be hedged. 17 / 57

18 Example: Oil derivatives We describe risk preferences by { Eexp[γc T ] if c t 0 for t < T, V(c) = + otherwise. where γ > 0 describes the risk aversion of the agent. The -problem can then be written minimize Eexp( γw T ) over x [0,q], where w T is given by the recursion c t +w t = r t w t 1 + (x l,k t c l,k t +x s,k t c s,k t ). k K This is a 288-dimensional convex optimization problem. 18 / 57

19 Example: Oil derivatives We discretized the probability measure with 10,000 scenarios generated by antithetic sampling. The approximate problem was solved with the sequential quadratic programming algorithm of Matlab s fmincon. The user can easily include other convex portfolio constraints coming e.g. from risk management. 19 / 57

20 Example: Oil derivatives 20 / 57

21 Example: Oil derivatives 21 / 57

22 Example: EONIA swaps EONIA (Euro Over Night Index Average) is the average overnight interest rate on agreed interbank lending. We study indifference swap rates of EONIA swaps (Overnight Index Swaps). The hedging instruments consist of EONIA and other EONIA swaps. This is joint work with Maria Nogueiras, HSBC. 22 / 57

23 Example: EONIA swaps Figure 2: Historical and simulated rates 23 / 57

24 Example: EONIA swaps Table 1: Swap data: OIS Maturity OIS Rate 1W E 3 2W E 3 3W E 3 1M E 3 2M E 3 3M E 3 6M E 3 24 / 57

25 Example: EONIA swaps We have C = {c M x N 0,z R K : x t +c t (1+r t )x t 1 + k Kz k c k t} where x t amount of overnight deposits, r t EONIA rate, c k,t net cash-flows of the kth swap, z k position in the kth swap (to be optimized). c t agent s cash-flows to be hedged, 25 / 57

26 Example: EONIA swaps We describe risk preferences by { Eexp[γc T ] if c t 0 for t < T, V(c) = + otherwise. where γ > 0 describes the risk aversion of the agent. The -problem can then be written as minimize Eexp( γx T ) over z R K, where x T is given by the recursion x t = (1+r t 1 )x t 1 + k Kz k c k,t c t. 26 / 57

27 Example: EONIA swaps Optimal terminal wealth distribution with γ = 1 27 / 57

28 Example: EONIA swaps Optimal terminal wealth distribution with γ = 5 28 / 57

29 Example: EONIA swaps Optimal terminal wealth distribution with γ = / 57

30 Pre-crisis valuations Risk neutral valuation assumes that the payout of a claim can be replicated by trading and that the negative of the trading strategy replicates the negative claim (perfect liquidity). It follows that there is only one sensible price for buying/selling the claim. the price can be expressed as the expectation of the cash-flows under a risk neutral measure. the price does not depend on our market expectations, risk preferences or financial position. The independence is peculiar to redundant securities whose cash-flows can be replicated by trading other assets. 30 / 57

31 Pre-crisis valuations Actuarial valuations come from the opposite direction where everything is invested on the bank account and nothing but fixed-income instruments can be replicated. Actuarial valuations can be divided roughly into premium principles reminiscent of indifference valuations discussed below. best estimate which is defined as the discounted expectation of future cash-flows. Such valuations are not market consistent: the best estimate of e.g. a European call tends to be too high. The best estimate is inherently procyclical: it increases when discount rates decrease during financial crises. A trick question: What discount rate should be used? 31 / 57

32 Pre-crisis valuations The flaws of pre-crisis valuations are well-known so it is common to adjust the incorrect valuations: Credit valuation adjustment (CVA) tries to correct for credit risk that was ignored by a pricing model. Funding valuation adjustment (FVA) tries to correct for incorrect lending/borrowing rates. Risk margin in Solvency II tries to correct for the the risk that is filtered out by the expectation in the best estimate.... Instead of adjusting incorrect valuations, we will adjust the underlying model and derive values from hedging arguments à la Black Scholes. 32 / 57

33 Valuation of contingent claims In incomplete markets, the hedging argument for valuation of contingent claims has two natural generalizations: accounting value: How much cash do we need to cover our liabilities at an acceptable level of risk? indifference price: What is the least price we can sell a financial product for without increasing our risk? The former is important in accounting, financial reporting and supervision (SII, IFRS) and in the BS-model. The latter is more relevant in trading. Classical math finance makes no distinction between the two. 33 / 57

34 Valuation of contingent claims In incomplete markets, the hedging argument for valuation of contingent claims has two natural generalizations: accounting value: How much cash do we need to cover our liabilities at an acceptable level of risk? indifference price: What is the least price we can sell a financial product for without increasing our risk? In general, such values depend on our views, risk preferences and financial position. Subjectivity is the driving force behind trading. Trying to avoid the subjectivity leads to inconsistencies and confusion. In complete markets, the two notions coincide and they are independent of the subjective factors 34 / 57

35 Accounting values Let ϕ : M R be the optimum value function of (). We define the accounting value for a liability c M by π 0 s(c) = inf{α R ϕ(c αp 0 ) 0} where p 0 = (1,0,...,0). Similarly, π 0 b(c) = sup{α R ϕ(αp 0 c) 0} gives the accounting value of an asset c M. π 0 s can be interpreted like a risk measure in [Artzner, Delbaen, Eber and Heath, 1999]. However, we have not assumed the existence of a cash-account so π 0 s is defined on sequences of cash-flows. 35 / 57

36 Accounting values Define the super- and subhedging costs π 0 sup(c) := inf{α c αp 0 C}, π 0 inf (c) := inf{α αp0 c C} Theorem 2 The accounting value π 0 s is convex and nondecreasing with respect to C. We have π 0 s π 0 sup and if π 0 s(0) 0, then π 0 inf (c) π0 b (c) π0 s(c) π 0 sup(c) with equalities throughout if c αp 0 C ( C) for α R. π 0 s is translation invariant : if c αp 0 C ( C ) (i.e. c M is replicable with initial cash α), then π 0 (c+c ) = π 0 (c)+α. In complete markets, c αp 0 C ( C ) always for some α R, so π 0 s(c) is independent of preferences and views. 36 / 57

37 Swap contracts In a swap contract, an agent receives a sequence p M of premiums and delivers a sequence c M of claims. Examples: Swaps with a fixed leg : p = (1,...,1), random c. In credit derivatives (CDS, CDO,...) and other insurance contracts, both p and c are random. Traditionally in mathematical finance, p = (1,0,...,0) and c = (0,...,0,c T ). Futures contracts: p = (0,...,0,1) and c = (0,...,0,c T ). Claims and premiums live in the same space M = {(c t ) T t=0 c t L 0 (Ω,F t,p;r)}. 37 / 57

38 Swap contracts Let ϕ : M R be the optimum value function of (). If we already have liabilities c M, then π( c,p;c) := inf{α R ϕ( c+c αp) ϕ( c)} gives the least swap rate that would allow us to enter a swap contract without worsening our financial position. Similarly, π b ( c,p;c) := sup{α R ϕ( c c+αp) ϕ( c)} = π( c,p; c) gives the greatest swap rate we would need on the opposite side of the trade. When p = (1,0,...,0) and c = (0,...,0,c T ), we get an extension of the indifference price of [Hodges and Neuberger, 1989] to nonproportional transactions costs. 38 / 57

39 Swap contracts Define the super- and subhedging swap rates, π sup (p;c) = inf{α c αp C }, π inf (p;c) = sup{α αp c C }. If C is a cone and p = (1,0,...,0), we recover the super- and subhedging costs π 0 sup and π 0 inf. Theorem 3 If π( c,p;0) 0, then π inf (p;c) π b ( c,p;c) π( c,p;c) π sup (p;c) with equalities if c αp C ( C ) for some α R. Agents with identical views, preferences and financial position have no reason to trade with each other. Prices are independent of such subjective factors when c αp C ( C ) for some α R. If in addition, p = p 0, then swap rates coincide with accounting values. 39 / 57

40 Swap contracts Example 4 (The classical model) Consider the classical perfectly liquid market model where C = {c M x N : T c t T 1 x t s t+1 } t=0 t=0 and C = C. The condition c αp C ( C ) holds if there exist x N such that T t=0 c t = α T p t + t=0 T 1 t=0 x t s t+1. The converse holds under the no-arbitrage condition. 40 / 57

41 Example: Oil derivatives The -problem again minimize Eexp( γw T ) over x [0,q], where w t = r t w t 1 + k K (x l,k t c l,k t +x s,k t c s,k t ) c t. Consider a forward contract where the trader receives the L barrels of Brent in December in exchange of a Lα units of cash in December. That is, c = (0,...,0,LS 1 12) and p = (0,...,0,L) The indifference swap rate π( c,p;c) = inf{α R ϕ( c+c αp) ϕ( c)} can be found by line search and numerical optimization. 41 / 57

42 Example: Oil derivatives The quoted bid forward rate for December Brent is up to 44 barrels. Line search and numerical optimization finds that the indifference price for going long L = 10 barrels is (this position can be perfectly hedged by the available December futures). L = 1000 barrels is (the optimal hedging strategy involves futures contracts with several maturities). 42 / 57

43 Example: EONIA swaps The -problem again: minimize Eexp( γx T ) over z R K, where x t = (1+r t 1 )x t 1 + k K z kc k,t c t. Consider a swap where the agent delivers a the floating leg c of an EONIA swap and receives a multiple p 1. The indifference swap rate π( c,p;c) = inf{α R ϕ( c+c αp) ϕ( c)} can be found by a simple line search with respect to α by computing the optimum value ϕ( c+c αp) at each iteration. 43 / 57

44 Example: EONIA swaps Reality check: The indifference rate of a quoted 6M swap equals the quoted rate This is independent of views and risk preferences just like the Black Scholes formula. Table 2: Optimal portfolios before and after the trade OIS Maturity before after 1W W W M M M M / 57

45 Example: EONIA swaps Indifference rate of an unquoted 100 day swap: Table 3: Optimal portfolios before and after the trade OIS Maturity before after 1W W W M M M M / 57

46 Example: EONIA swaps Table 4: Dependence of indifference rate on the initial cash position units of cash ID rate / 57

47 In practice, many contracts and products involve optionalities: American options, Callable bonds, Swing options, Delivery contracts, Storages,... In general, a long position in a contract with optionalities allows an agent to choose a sequence of cash-flows within a given (possibly random) set C R T+1. Example: an American option on an underlying X = (X t ) T t=0 : T C = {c c ex, e 0, e t 1, e t {0,1}}. The indifference swap rate for a long position in C becomes t=0 π l ( c,p;c) = sup{α inf ϕ( c c+αp) ϕ( c)}, c M(C) where M(C) denotes the (F t ) T t=0-adapted selectors of C. 47 / 57

48 Long positions in a contract with optionalities can be treated mathematically and numerically much like nonoptional contracts. Quantitative analysis of a short position requires a model for the behaviour (exercise strategy) of the counterparty. The mathematical literature on American options concentrates on superhedging against the worst case. In practice, superhedging and the worst case assumption often lead to excessively high prices. Indifference pricing of both long and short positions is studied in [Koch Medona, Munari, Pennanen, 2016]. 48 / 57

49 Embedding optimal investment problems in the general Conjugate duality framework of [Rockafellar, 1974] yields extensions of many classical duality results from financial mathematics to more general problems with e.g. illiquidity effects, transaction costs, portfolio constraints,... Combined with certain measure theoretic results from financial mathematics, convex analysis allows for closing the duality gap in quite a general class of models. In particular, in the classical perfectly liquid market model, we obtain a simple derivation of the sharpest form of the fundamental theorem of asset pricing due to [Dalang, Morton and Willinger, 1992]. 49 / 57

50 Let M p = {c M c t L p (Ω,F t,p;r)}. The bilinear form T c,y := E c t y t t=0 puts M 1 and M in separating duality. The conjugate of a function f on M 1 is defined by f (y) = sup c M 1 { c,y f(c)}. If f is proper, convex and lower semicontinuous, then f(y) = sup y M { c,y f (y)}. 50 / 57

51 We assume from now on that T V(c) = E V t (c t ) t=0 for convex random functions V t : R Ω R with V t (0) = 0. Theorem 5 If S t (x, ) L 1 for all x R J, then ϕ (y) = V (y)+σ C (y) where V (y) = E T t=0 V t (y t ) and σ C (y) = sup c C c,y. Moreover, T σ C (y) = inf v N 1E [(y t S t ) (v t )+σ Dt (E[ v t+1 F t ])] t=0 where the infimum is attained for all y M. 51 / 57

52 Example 6 If S t (ω,x) = s t (ω) x and D t (ω) is a cone, C = {y M E[ (y t+1 s t+1 ) F t ] D t}. Example 7 If S t (ω,x) = sup{s x s [s b t(ω),s a t(ω)]} and D t (ω) = R J, then C = {y M ys is a martingale for some s [s b,s a ]}. Example 8 In the classical model, C consists of positive multiples of martingale densities. 52 / 57

53 Theorem 9 Assume the linearity condition, the Inada condition V t = δ R and that p 0 / C and infϕ < 0. Then π 0 (c) = sup y M { c,y σ C (y) σ B (y) y 0 = 1}, where B = {c M 1 V(c) 0}. In particular, when C is conical and V is positively homogeneous, π 0 (c) = sup y M { c,y y C B, y 0 = 1}. Extends good deal bounds to sequences of cash-flows. 53 / 57

54 Theorem 10 Assume the linearity condition, the Inada condition and that p / C and infϕ < ϕ( c). Then π( c,p;c) = sup y M { c,y σc (y) σ B( c) (y) p,y = 1 }, where B( c) = {c M 1 V( c+c) ϕ( c)}. In particular, if C is conical, π( c,p;c) = sup y M { c,y σb( c) (y) u C, p,y = 1 }. 54 / 57

55 Example 11 In the classical model, with p = (1,0,...,0) and V t = δ R for t < T, we get T π( c,p;c) = sup sup Q Q α>0e Q{ [ ( c t +c t ) α VT( dq ] } dp /α) ϕ( c) t=0 where Q is the set of absolutely continuous martingale measures; see [Biagini, Frittelli, Grasselli, 2011] for a continuous-time version. 55 / 57

56 Theorem 12 (FTAP) Assume that S is finite-valued and that D R J. Then the following are equivalent 1. S satisfies the robust no-arbitrage condition. 2. There is a strictly consistent price system: adapted processes y and s such that y > 0, s t ridoms t and ys is a martingale. In the classical linear market model, ridoms t = {1, s t } so we recover the Dalang Morton Willinger theorem. The robust no-arbitrage condition means that there exists a sublinear arbitrage-free cost process S with dom S t ridoms t. 56 / 57

57 Summary Post-crisis FM is subjective: optimal investment and valuations depend on views, risk preferences, financial position and trading expertise. brings pricing, accounting and risk management under a single consistent framework. Not a quick solution but a coherent and universal approach based on risk management. Requires techniques from statistics, optimization, and computer science. With some convex analysis, classical fundamental theorems can be extended to illiquid market models. 57 / 57