### 统计代写|离散时间鞅理论代写martingale代考|Model-independent options

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• Statistical Inference 统计推断
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• (Generalized) Linear Models 广义线性模型
• Statistical Machine Learning 统计机器学习
• Longitudinal Data Analysis 纵向数据分析
• Foundations of Data Science 数据科学基础

## 统计代写|离散时间鞅理论代写martingale代考|Probabilistic setup

This chapter requires some basic knowledge in stochastic analysis (not so much, mainly stochastic integration and Itô’s formula).

As in Chapter 2, we assume a zero interest rate (non-zero rates are briefly considered in Section 3.3.4). The price of an asset at time $t,\left(S_{t}\right){t \in[0, T]}$, will be modeled by a continuous semi-martingales. The semi-martingale property is imposed as we want to give a meaning to the limit when $n \rightarrow \infty$ of the discrete delta-hedging $$\sum{t_{0}=0}^{T} H_{t_{i}}\left(S_{t_{i+1}}-S_{t_{i}}\right) \stackrel{n \rightarrow \infty}{\longrightarrow} \int_{0}^{T} H_{t} d S_{t}$$
Good integrator processes are precisely provided by semi-martingales. Below, we describe our probabilistic framework.

Let $\Omega \equiv\left{\omega \in C\left([0, T], \mathbb{R}{+}\right): \omega{0}=0\right}$ be the canonical space equipped with the uniform norm $|\omega|_{\infty} \equiv \sup {0 \leq t \leq T}|\omega(t)|, B$ the canonical process, i.e., $B{t}(\omega) \equiv \omega(t)$ and $\mathcal{F} \equiv\left{\mathcal{F}{t}\right}{0 \leq t \leq T}$ the filtration generated by $B$ : $\mathcal{F}{t}=$ $\sigma\left{B{s}, s \leq t\right} . \mathbb{P O}$ is the Wiener measure. $S_{0}$ is some given initial value in $\mathbb{R}{+}$, and we denote $$S{t} \equiv S_{0}+B_{t} \text { for } t \in[0, T] .$$
For any $\mathcal{F}$-adapted process $\sigma$ and satisfying $\int_{0}^{T} \sigma_{s}^{2} d s<\infty, \mathbb{P}^{0}$-a.s., we define the probability measure on $(\Omega, \mathcal{F})$ :
$$\mathbb{P}^{\sigma} \equiv \mathbb{P}^{0} \circ\left(S^{\sigma}\right)^{-1} \text { where } S_{t}^{\sigma} \equiv S_{0}+\int_{0}^{t} \sigma_{r} d B_{r}, t \in[0, T], \mathbb{P}^{0}-\text { a.s. }$$

## 统计代写|离散时间鞅理论代写martingale代考|Variance swaps

It is well-known that the process $\ln S_{t}+\frac{1}{2}\langle\ln S\rangle_{t}$ is a martingale. As an important consequence in finance, this leads to the exact replication of a

variance swap (within the class $\mathcal{M}^{c}$ ) in terms of a log-contract. A discretemonitoring variance swap pays at a maturity $T$ the sum of daily squared log-returns, mainly
$$\frac{1}{T} \sum_{i=0}^{n-1}\left(\ln \frac{S_{t_{i+1}}}{S_{t_{i}}}\right)^{2}, \quad t_{0}=0, \quad t_{n}=T$$
and $\Delta t=t_{i+1}-t_{i}=$ one day. In the limit $n \rightarrow \infty$, it converges $\mathbb{P}$-almost surely to the quadratic variation $\langle\ln S\rangle_{T}$ of $\ln S$ :
$$\frac{1}{T} \sum_{i=0}^{n-1}\left(\ln \frac{S_{t_{i+1}}}{S_{t_{i}}}\right)^{2} \stackrel{n \rightarrow \infty}{\longrightarrow} \frac{1}{T}\langle\ln S\rangle_{T}$$
REMARK 3.1 Note that in practice, $t_{k+1}-t_{k}=1$ day and the approximation of a discrete-monitored variance swap by its continuous-time version is valid. Indeed,
$$\mathrm{VS} \equiv \frac{1}{T} \sum_{i=0}^{n-1} \mathbb{E}\left[\left(\ln \frac{S_{t_{i+1}}}{S_{t_{i}}}\right)^{2}\right]=\frac{1}{T} \sum_{i=0}^{n-1} \mathbb{E}\left[\left(-\frac{1}{2}\left(\sigma_{t_{i}}^{\mathrm{LN}}\right)^{2} \Delta t+\sigma_{t_{i}}^{\mathrm{LN}} \Delta B_{t_{i}}\right)^{2}\right]$$
where $\sigma_{t_{i}}^{\mathrm{LN}}$ is the realized (log-normal) volatility between $\left[t_{i}, t_{i+1}\right], \Delta B_{t_{i}} \equiv$ $B_{t_{i+1}}-B_{t_{i}}$ and $T=n \Delta t$. This gives
$$\mathrm{VS} \equiv \frac{1}{T} \sum_{i=0}^{n-1} \mathbb{E}\left[\left(\frac{1}{4}\left(\sigma_{t_{i}}^{\mathrm{LN}}\right)^{4}(\Delta t)^{2}+\left(\sigma_{t_{i}}^{\mathrm{LN}}\right)^{2} \Delta t\right)\right]$$
By taking $\sigma_{t_{i}}^{\mathrm{LN}}=\sigma^{\mathrm{LN}}$ constant, we get
$$\sqrt{\mathrm{VS}} \equiv\left(\sigma^{\mathrm{LN}}\right)\left(1+\frac{1}{4}\left(\sigma^{\mathrm{LN}}\right)^{2} \Delta t\right)^{\frac{1}{2}}$$
If we impose a relative error of $10^{-3}$ between the continuous and the discrete version, we obtain $\Delta t=810^{-3} /\left(\sigma^{\mathrm{LN}}\right)^{2}$. For $\sigma^{\mathrm{LN}} \sim 100 \%$, we get $\Delta t \approx 3$ days.

## 统计代写|离散时间鞅理论代写martingale代考|Covariance options

We consider two liquid European options with payoffs $F_{1}$ and $F_{2}$ and maturity $T$, possibly depending on different assets. We denote $\mathbb{E}{t}^{\mathbb{P}}\left[F{1}\right]$ (resp. $\mathbb{E}{t}^{\mathbb{P}}\left[F{2}\right]$ ) the $t$-value of this option quoted on the market. The market uses a priori two (different) risk-neutral probability measures $\mathbb{P}^{1}$ and $\mathbb{P}^{2}$. We will assume

that they coincide and belong to $\mathcal{M}^{c}$. $\mathbb{P}$ is not known, we have only a partial characterization through the values $\mathbb{E}{t}^{\mathbb{P}}\left[F{1}\right]$ and $\mathbb{E}{t}^{\mathbb{P}}\left[F{2}\right]$. We assume also that the payoff $F_{1} F_{2}$ with maturity $T$ can be bought at $t=0$ with market prices $\mathbb{E}^{\mu}\left[F_{1} F_{2}\right]$

A covariance option pays at a maturity $T$ the daily realized covariance between the prices $\mathbb{E}{t}^{\mathbb{P}}\left[F{1}\right]$ and $\mathbb{E}{t}^{\mathbb{P}}\left[F{2}\right]$ :
$$\sum_{i=0}^{n-1}\left(\mathbb{E}{t{i+1}}^{\mathbb{P}}\left[F_{1}\right]-\mathbb{E}{t{i}}^{\mathbb{P}}\left[F_{1}\right]\right)\left(\mathbb{E}{t{i+1}}^{P}\left[F_{2}\right]-\mathbb{E}{t{i}}^{\mathbb{P}}\left[F_{2}\right]\right)$$
In the limit $n \rightarrow \infty$, it converges to
$$\int_{0}^{T} d\left\langle\mathbb{E}^{\mathbb{P}}\left[F_{1}\right], \mathbb{E}^{\mathbb{P}}\left[F_{2}\right]\right\rangle_{t}$$
From Itô’s lemma, we have for all $\mathbb{P} \in \mathcal{M}^{c}$ :
$$\begin{array}{r} \int_{0}^{T} d\left\langle\mathbb{E}^{\mathrm{P}}\left[F_{1}\right], \mathbb{E}^{\mathrm{P}}\left[F_{2}\right]\right\rangle_{t}=\left(F_{1} F_{2}-\mathbb{E}^{\mu}\left[F_{1} F_{2}\right]\right) \ +\left(\mathbb{E}^{\mu}\left[F_{1} F_{2}\right]-\mathbb{E}{0}^{\mathbb{P}}\left[F{1}\right] \mathbb{E}{0}^{\mathbb{P}}\left[F{2}\right]\right) \ -\int_{0}^{T} \mathbb{E}{t}^{\mathbb{P}}\left[F{1}\right] d \mathbb{E}{t}^{\mathbb{P}}\left[F{2}\right]-\int_{0}^{T} \mathbb{E}{t}^{\mathbb{P}}\left[F{2}\right] d \mathbb{E}{t}^{\mathbb{P}}\left[F{1}\right] \end{array}$$
As observed in $[76]$, this equality indicates that a covariance option can be replicated by doing a delta-hedging on $\mathbb{E}{t}^{\mathbb{P}}\left[F{1}\right]$ (resp. $\mathbb{E}{t}^{\mathbb{P}}\left[F{2}\right]$ ) with $H_{t}^{1} \equiv$ $-\mathbb{E}{t}^{\mathbb{P}}\left[F{2}\right]$ (resp. $H_{t}^{2} \equiv-\mathbb{E}{t}^{\mathrm{P}}\left[F{1}\right]$ ) and statically holding the $T$-European payoff $F_{1} F_{2}$ with market price $\mathbb{E}^{\mu}\left[F_{1} F_{2}\right]$. The model-independent price of this option is therefore
\begin{aligned} \mathbb{E}^{\mathbb{P}}\left[\int_{0}^{T} d\left\langle\mathbb{E}^{\mathbb{P}}\left[F_{1}\right], \mathbb{E}^{\mathbb{P}}\left[F_{2}\right]\right\rangle_{t}\right]=& \mathbb{E}^{\mu}\left[F_{1} F_{2}\right]-\mathbb{E}{0}^{\mathbb{P}}\left[F{1}\right] \mathbb{E}{0}^{\mathbb{P}}\left[F{2}\right] \ & \forall \mathbb{P} \in \mathcal{M}^{c} \cap\left{\mathbb{P}: \mathbb{E}^{\mathbb{P}}\left[F_{1} F_{2}\right]=\mathbb{E}^{\mu}\left[F_{1} F_{2}\right]\right} \end{aligned}

## 统计代写|离散时间鞅理论代写martingale代考|Probabilistic setup

∑吨0=0吨H吨一世(小号吨一世+1−小号吨一世)⟶n→∞∫0吨H吨d小号吨

## 统计代写|离散时间鞅理论代写martingale代考|Variance swaps

1吨∑一世=0n−1(ln⁡小号吨一世+1小号吨一世)2,吨0=0,吨n=吨

1吨∑一世=0n−1(ln⁡小号吨一世+1小号吨一世)2⟶n→∞1吨⟨ln⁡小号⟩吨

## 统计代写|离散时间鞅理论代写martingale代考|Covariance options

∑一世=0n−1(和吨一世+1磷[F1]−和吨一世磷[F1])(和吨一世+1磷[F2]−和吨一世磷[F2])

∫0吨d⟨和磷[F1],和磷[F2]⟩吨

∫0吨d⟨和磷[F1],和磷[F2]⟩吨=(F1F2−和μ[F1F2]) +(和μ[F1F2]−和0磷[F1]和0磷[F2]) −∫0吨和吨磷[F1]d和吨磷[F2]−∫0吨和吨磷[F2]d和吨磷[F1]

\begin{对齐} \mathbb{E}^{\mathbb{P}}\left[\int_{0}^{T} d\left\langle\mathbb{E}^{\mathbb{P}}\left [F_{1}\right], \mathbb{E}^{\mathbb{P}}\left[F_{2}\right]\right\rangle_{t}\right]=& \mathbb{E}^ {\mu}\left[F_{1} F_{2}\right]-\mathbb{E}{0}^{\mathbb{P}}\left[F{1}\right] \mathbb{E} {0}^{\mathbb{P}}\left[F{2}\right] \ & \forall \mathbb{P} \in \mathcal{M}^{c} \cap\left{\mathbb{P }: \mathbb{E}^{\mathbb{P}}\left[F_{1} F_{2}\right]=\mathbb{E}^{\mu}\left[F_{1} F_{2 }\right]\right} \end{对齐}\begin{对齐} \mathbb{E}^{\mathbb{P}}\left[\int_{0}^{T} d\left\langle\mathbb{E}^{\mathbb{P}}\left [F_{1}\right], \mathbb{E}^{\mathbb{P}}\left[F_{2}\right]\right\rangle_{t}\right]=& \mathbb{E}^ {\mu}\left[F_{1} F_{2}\right]-\mathbb{E}{0}^{\mathbb{P}}\left[F{1}\right] \mathbb{E} {0}^{\mathbb{P}}\left[F{2}\right] \ & \forall \mathbb{P} \in \mathcal{M}^{c} \cap\left{\mathbb{P }: \mathbb{E}^{\mathbb{P}}\left[F_{1} F_{2}\right]=\mathbb{E}^{\mu}\left[F_{1} F_{2 }\right]\right} \end{对齐}

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