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Martingles

鞅(martingale),2.2. Conditional expectations

In probability theory, a martingale is a sequence of random variables (i.e., a stochastic process) for which, at a particular time, the conditional expectation of the next value in the sequence is equal to the present value, regardless of all prior values.   See more martingale: [noun] a device for steadying a horse's head or checking its upward movement that typically consists of a strap fastened to the girth, passing between the forelegs, and bifurcating 06/06/ · In the gambling world such a system is called a martingale, which explains the origin of the mathematical term "martingale". One of the basic facts of the theory of martingales is Examples of martingales. Let X t+1 = X t ± b t where +b t and -b t occur with equal probability b t is measurable ℱ t, and the outcome ±b t is measurable ℱ t+1 (in other words, my A martingale is a class of betting strategies that originated from and were popular in 18th-century France. The simplest of these strategies was designed for a game in which the gambler wins ... read more

What you see is a random variable with only 11 values the possible sums You can detect whether some events occured "is the sum even? Filtrations With a stochastic process, it is natural to talk not only about the value of the process at time t which is just the random variable X t , but also what we know at time t. In practice, we are never going to actually do this.

We won't prove these facts here, see e. We can think of this process as describing the state of our finances after we've been playing in a casino for a while. If the casino is perfectly fair unlike what happens in real life , then each bet we place should have an expected return of 0.

But this local property has strong consequences that apply across long intervals of time, as we will see below. Special case: A random ±1 walk is a martingale. So {Y t } is a martingale. What about E[X t ], with no conditioning? In other words, martingales never go anywhere, at least in expectation. We can apply this to the martingales we've seen so far: For an arbitrary betting strategy on a fair game, I neither make nor lose money on average.

This is probably a bad strategy for ordinary people but it works out well for insurance companies, who charge a small additional premium to make a profit above the zero expected return. Then we can write X t as , where E[Δ i Δ In other words, Δ i is uncorrelated with Δ Δ i This is not quite as good a condition as independence, but is good enough that martingales often act very much like sums of independent random variables.

But in fact we can do much better by using moment generating functions; the result is an inequality known as the Azuma-Hoeffding inequality named for its independent co-discoverers , which is the martingale version of Chernoff bounds.

See Azuma-Hoeffding inequality. Application: the method of bounded differences Basic idea: Azuma-Hoeffding applies to any process that we can model as revealing the inputs x x n to some function f x x n one at a time, provided changing any one input changes f by at most c the Lipschitz condition.

The reason is that when the Lipschitz condition holds, then E[f x x t ] is a martingale that satisfies the requirements of the inequality. This allows us to show, for example, that the number of colors needed to color a random graph is tightly concentrated, by considering a process where x i reveals all the edges between vertex i and smaller vertices a vertex exposure martingale.

In simple terms, T is a stopping time if you know at time t whether you've stopped or not. The first condition says that T is finite with probability 1 i.

The second condition puts a bound on how big X T can get, which excludes some bad outcomes where we accept a small probability of a huge loss in order to get a large probability of a small gain. So now we'll prove the full version by considering E[X min T,n ] and showing that, under the conditions of the theorem, it approaches E[X T ] as n goes to infinity. If we can show that the middle term also vanishes in the limit, we are done.

Here we use condition 2. n converges to E[X T ]. So the middle term goes to zero as n goes to infinity. This completes the proof. Using the full-blown optional stopping theorem is a pain in the neck, because conditions 2 and 3 are often hard to test directly.

Let T be the time at which the process stops. We have bounded increments by the definition of the process bounded range also works. Again we have bounded increments but not bounded range! Note that the quantity that is "sub" below or "super" above is always where we are now: so submartingales tend to go up over time while supermartingales tend to go down. This disambiguation page lists articles associated with the title Martingale.

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The Martingale system is a system of investing in which the dollar value of investments continually increases after losses, or the position size increases with the lowering portfolio size. The Martingale system was introduced by French mathematician Paul Pierre Levy in the 18th century.

The strategy is based on the premise that only one good bet or trade is needed to turn your fortunes around. This technique can be contrasted with the anti-martingale system , which involves halving a bet each time there is a trade loss and doubling it each time there is a gain.

The Martingale system is a risk-seeking method of investing. The main idea behind the Martingale system is that statistically, you cannot lose all of the time, and thus you should increase the amount allocated in investments—even if they are declining in value—in anticipation of a future increase. Martingale strategies rely on the theory of mean reversion.

Without a plentiful supply of money to obtain positive results, you need to endure missed trades that can bankrupt an entire account. It's also important to note that the amount risked on the trade is far higher than the potential gain. Despite these drawbacks, there are ways to improve the martingale strategy that can boost your chances of succeeding. The Martingale system is commonly compared to betting in a casino with the hopes of breaking even. When a gambler who uses this method experiences a loss, they immediately double the size of the next bet.

By repeatedly doubling the bet when they lose, the gambler, in theory, will eventually even out with a win. This assumes the gambler has an unlimited supply of money to bet with, or at least enough money to make it to the winning payoff. Indeed, just a few successive losses under this system could lead to losing everything you came with.

To understand the basics behind the strategy, let's look at a basic example. There is an equal probability that the coin will land on heads or tails, and each flip is independent. The prior flip does not impact the outcome of the next flip. Martingale trading a popular strategy in the forex markets. One of the reasons the martingale strategy is so popular in the currency market is that currencies, unlike stocks , rarely drop to zero.

Although companies can easily go bankrupt, most countries only do so by choice. There will be times when a currency falls in value. However, even in cases of a sharp decline , the currency's value rarely reaches zero.

The FX market also offers another advantage that makes it more attractive for traders who have the capital to follow the martingale strategy. The ability to earn interest allows traders to offset a portion of their losses with interest income.

That means an astute martingale trader may want to use the strategy on currency pairs in the direction of positive carry. In other words, they would borrow using a low-interest rate currency and buy a currency with a higher interest rate. Trading Psychology. Company News Markets News Cryptocurrency News Personal Finance News Economic News Government News.

Your Money. Personal Finance. Your Practice. Popular Courses. Investing Portfolio Management. What Is the Martingale System? Key Takeaways The Martingale system is a methodology to amplify the chance of recovering from losing streaks. The Martingale strategy involves doubling up on losing bets and reducing winning bets by half. It essentially a strategy that promotes a loss-averse mentality that tries to improve the odds of breaking even, but also increases the chances of severe and quick losses.

Forex trading is more well-suited to this type of strategy than for stocks trading or casino gambling. Compare Accounts. Advertiser Disclosure ×.

The offers that appear in this table are from partnerships from which Investopedia receives compensation. This compensation may impact how and where listings appear. Investopedia does not include all offers available in the marketplace. Related Terms. Anti-Martingale System Definition The anti-Martingale system is a trading method that involves halving a bet each time there is a trade loss, and doubling it each time there is a gain.

Pip Definition, Calculation, and Examples A pip is the smallest price increment fraction tabulated by currency markets to establish the price of a currency pair. Gambling Loss A gambling loss is a loss resulting from risking money or other stakes on games of chance or wagering events with uncertain outcomes.

Parlay bets are a combination of individual wagers In sports betting, a parlay bet is a bet made up of two or more individual wagers. Combining bets makes them harder to win but increases their payout. Expected Utility Expected utility is an economic term summarizing the utility that an entity or aggregate economy is expected to reach under any number of circumstances.

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Martingale System,2.1. Filtrations

A martingale is a class of betting strategies that originated from and were popular in 18th-century France. The simplest of these strategies was designed for a game in which the gambler wins 28/01/ · Summary. The Martingale Strategy is a strategy of investing or betting introduced by French mathematician Paul Pierre Levy. It is considered a risky method of investing. It is In probability theory, a martingale is a sequence of random variables (i.e., a stochastic process) for which, at a particular time, the conditional expectation of the next value in the sequence is equal to the present value, regardless of all prior values.   See more 鞅 (martingale) 则称它为鞅过程,简称鞅。. 鞅是公平博弈的广义版本。. 因为若我们将 Z_n 解释为一个赌徒在第 n 次赌博后的财产,则式 (1)说明无论前面发生了什么,他在第 n+1 次赌博后的 Martingales. Definitions and properties The theory of martingales plays a very important ans ueful role in the study of stochastic processes. A formal definition is given below. 06/06/ · In the gambling world such a system is called a martingale, which explains the origin of the mathematical term "martingale". One of the basic facts of the theory of martingales is ... read more

Following is an analysis of the expected value of one round. Martingale trading a popular strategy in the forex markets. See: Gambling terminology. Main article: Stopping time. Skorohod, "The theory of stochastic processes" , 1 , Springer Translated from Russian MR Zbl

Here we use condition 2. Meyer, martingles, "Probabilities and potential"1—3North-Holland — pp, martingles. So the middle term goes to zero as n goes to infinity. Additive process Bessel process Birth—death process pure birth Brownian motion Bridge Excursion Fractional Geometric Meander Cauchy martingles Contact process Continuous-time random walk Cox process Diffusion process Empirical process Feller process Fleming—Viot process Gamma process Geometric process Hawkes process Hunt process Interacting particle systems Itô diffusion Itô process Martingles diffusion Jump process Lévy process Local time Markov additive process McKean—Vlasov process Ornstein—Uhlenbeck process Poisson process Compound Non-homogeneous Schramm—Loewner evolution Semimartingale Sigma-martingale Martingles process Superprocess Telegraph process Variance gamma process Wiener process Wiener sausage. The second condition puts a bound on how big X T can get, martingles, which excludes some bad outcomes where we accept a small probability of a huge loss in order to get a large probability of a small gain. We have bounded increments by the definition of the process bounded range also works. What links here Related changes Upload file Special pages Permanent link Page martingles Cite this page Wikidata item, martingles.

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