Algorithmic trading is a method of executing a large order too large to fill all at once using automated pre-programmed trading instructions accounting for variables such as time, price, and volume  to send small slices of the order child orders out to the market over time. They were developed so that traders do not need to constantly watch a stock and repeatedly send those slices out manually.
In the past several years algo trading has been gaining traction with both retails and institutional traders. Algorithmic trading is not an attempt to make a trading profit. It is simply a way to minimise the cost, market impact and risk in execution of an order. The term is also used to mean automated trading system. These do indeed have the goal of making a profit. Also known as black box trading , these encompass trading strategies that are heavily reliant on complex mathematical formulas and high-speed computer programs.
Such systems run strategies including market making , inter-market spreading, arbitrage , or pure speculation such as trend following. Many fall into the category of high-frequency trading HFT , which are characterized by high turnover and high order-to-trade ratios. Algorithmic trading and HFT have resulted in a dramatic change of the market microstructure , particularly in the way liquidity is provided.
In March , Virtu Financial , a high-frequency trading firm, reported that during five years the firm as a whole was profitable on 1, out of 1, trading days,  losing money just one day, empirically demonstrating the law of large numbers benefit of trading thousands to millions of tiny, low-risk and low-edge trades every trading day.
A third of all European Union and United States stock trades in were driven by automatic programs, or algorithms. Algorithmic trading and HFT have been the subject of much public debate since the U. Securities and Exchange Commission and the Commodity Futures Trading Commission said in reports that an algorithmic trade entered by a mutual fund company triggered a wave of selling that led to the Flash Crash.
As a result of these events, the Dow Jones Industrial Average suffered its second largest intraday point swing ever to that date, though prices quickly recovered. A July, report by the International Organization of Securities Commissions IOSCO , an international body of securities regulators, concluded that while "algorithms and HFT technology have been used by market participants to manage their trading and risk, their usage was also clearly a contributing factor in the flash crash event of May 6, In practice this means that all program trades are entered with the aid of a computer.
At about the same time portfolio insurance was designed to create a synthetic put option on a stock portfolio by dynamically trading stock index futures according to a computer model based on the Black—Scholes option pricing model. Both strategies, often simply lumped together as "program trading", were blamed by many people for example by the Brady report for exacerbating or even starting the stock market crash.
Yet the impact of computer driven trading on stock market crashes is unclear and widely discussed in the academic community. Financial markets with fully electronic execution and similar electronic communication networks developed in the late s and s. This increased market liquidity led to institutional traders splitting up orders according to computer algorithms so they could execute orders at a better average price. These average price benchmarks are measured and calculated by computers by applying the time-weighted average price or more usually by the volume-weighted average price.
A further encouragement for the adoption of algorithmic trading in the financial markets came in when a team of IBM researchers published a paper  at the International Joint Conference on Artificial Intelligence where they showed that in experimental laboratory versions of the electronic auctions used in the financial markets, two algorithmic strategies IBM's own MGD , and Hewlett-Packard 's ZIP could consistently out-perform human traders.
As more electronic markets opened, other algorithmic trading strategies were introduced. These strategies are more easily implemented by computers, because machines can react more rapidly to temporary mispricing and examine prices from several markets simultaneously. For example, Chameleon developed by BNP Paribas , Stealth  developed by the Deutsche Bank , Sniper and Guerilla developed by Credit Suisse  , arbitrage , statistical arbitrage , trend following , and mean reversion.
This type of trading is what is driving the new demand for low latency proximity hosting and global exchange connectivity.
It is imperative to understand what latency is when putting together a strategy for electronic trading. Latency refers to the delay between the transmission of information from a source and the reception of the information at a destination. Latency is, as a lower bound, determined by the speed of light; this corresponds to about 3. Any signal regenerating or routing equipment introduces greater latency than this lightspeed baseline.
Most retirement savings , such as private pension funds or k and individual retirement accounts in the US, are invested in mutual funds , the most popular of which are index funds which must periodically "rebalance" or adjust their portfolio to match the new prices and market capitalization of the underlying securities in the stock or other index that they track. Pairs trading or pair trading is a long-short, ideally market-neutral strategy enabling traders to profit from transient discrepancies in relative value of close substitutes.
Unlike in the case of classic arbitrage, in case of pairs trading, the law of one price cannot guarantee convergence of prices. This is especially true when the strategy is applied to individual stocks — these imperfect substitutes can in fact diverge indefinitely. In theory the long-short nature of the strategy should make it work regardless of the stock market direction. In practice, execution risk, persistent and large divergences, as well as a decline in volatility can make this strategy unprofitable for long periods of time e.
It belongs to wider categories of statistical arbitrage , convergence trading , and relative value strategies. In finance, delta-neutral describes a portfolio of related financial securities, in which the portfolio value remains unchanged due to small changes in the value of the underlying security. Such a portfolio typically contains options and their corresponding underlying securities such that positive and negative delta components offset, resulting in the portfolio's value being relatively insensitive to changes in the value of the underlying security.
When used by academics, an arbitrage is a transaction that involves no negative cash flow at any probabilistic or temporal state and a positive cash flow in at least one state; in simple terms, it is the possibility of a risk-free profit at zero cost. During most trading days these two will develop disparity in the pricing between the two of them. Arbitrage is not simply the act of buying a product in one market and selling it in another for a higher price at some later time.
The long and short transactions should ideally occur simultaneously to minimize the exposure to market risk, or the risk that prices may change on one market before both transactions are complete. In practical terms, this is generally only possible with securities and financial products which can be traded electronically, and even then, when first leg s of the trade is executed, the prices in the other legs may have worsened, locking in a guaranteed loss. Missing one of the legs of the trade and subsequently having to open it at a worse price is called 'execution risk' or more specifically 'leg-in and leg-out risk'.
In the simplest example, any good sold in one market should sell for the same price in another. Traders may, for example, find that the price of wheat is lower in agricultural regions than in cities, purchase the good, and transport it to another region to sell at a higher price.
This type of price arbitrage is the most common, but this simple example ignores the cost of transport, storage, risk, and other factors. Where securities are traded on more than one exchange, arbitrage occurs by simultaneously buying in one and selling on the other. Such simultaneous execution, if perfect substitutes are involved, minimizes capital requirements, but in practice never creates a "self-financing" free position, as many sources incorrectly assume following the theory.
As long as there is some difference in the market value and riskiness of the two legs, capital would have to be put up in order to carry the long-short arbitrage position. Mean reversion is a mathematical methodology sometimes used for stock investing, but it can be applied to other processes. In general terms the idea is that both a stock's high and low prices are temporary, and that a stock's price tends to have an average price over time. An example of a mean-reverting process is the Ornstein-Uhlenbeck stochastic equation.
Mean reversion involves first identifying the trading range for a stock, and then computing the average price using analytical techniques as it relates to assets, earnings, etc. When the current market price is less than the average price, the stock is considered attractive for purchase, with the expectation that the price will rise.
When the current market price is above the average price, the market price is expected to fall. In other words, deviations from the average price are expected to revert to the average. The standard deviation of the most recent prices e.
Stock reporting services such as Yahoo! Finance, MS Investor, Morningstar, etc. While reporting services provide the averages, identifying the high and low prices for the study period is still necessary.
Scalping is liquidity provision by non-traditional market makers , whereby traders attempt to earn or make the bid-ask spread. This procedure allows for profit for so long as price moves are less than this spread and normally involves establishing and liquidating a position quickly, usually within minutes or less. A market maker is basically a specialized scalper. The volume a market maker trades is many times more than the average individual scalper and would make use of more sophisticated trading systems and technology.
However, registered market makers are bound by exchange rules stipulating their minimum quote obligations. For instance, NASDAQ requires each market maker to post at least one bid and one ask at some price level, so as to maintain a two-sided market for each stock represented. Most strategies referred to as algorithmic trading as well as algorithmic liquidity-seeking fall into the cost-reduction category. The basic idea is to break down a large order into small orders and place them in the market over time.
The choice of algorithm depends on various factors, with the most important being volatility and liquidity of the stock. For example, for a highly liquid stock, matching a certain percentage of the overall orders of stock called volume inline algorithms is usually a good strategy, but for a highly illiquid stock, algorithms try to match every order that has a favorable price called liquidity-seeking algorithms.
The success of these strategies is usually measured by comparing the average price at which the entire order was executed with the average price achieved through a benchmark execution for the same duration.
Usually, the volume-weighted average price is used as the benchmark. At times, the execution price is also compared with the price of the instrument at the time of placing the order. A special class of these algorithms attempts to detect algorithmic or iceberg orders on the other side i.
These algorithms are called sniffing algorithms. A typical example is "Stealth. Modern algorithms are often optimally constructed via either static or dynamic programming. Recently, HFT, which comprises a broad set of buy-side as well as market making sell side traders, has become more prominent and controversial. When several small orders are filled the sharks may have discovered the presence of a large iceberged order. Strategies designed to generate alpha are considered market timing strategies.
These types of strategies are designed using a methodology that includes backtesting, forward testing and live testing. Market timing algorithms will typically use technical indicators such as moving averages but can also include pattern recognition logic implemented using Finite State Machines. Backtesting the algorithm is typically the first stage and involves simulating the hypothetical trades through an in-sample data period. Optimization is performed in order to determine the most optimal inputs.
Forward testing the algorithm is the next stage and involves running the algorithm through an out of sample data set to ensure the algorithm performs within backtested expectations. Live testing is the final stage of development and requires the developer to compare actual live trades with both the backtested and forward tested models. Metrics compared include percent profitable, profit factor, maximum drawdown and average gain per trade.
As noted above, high-frequency trading HFT is a form of algorithmic trading characterized by high turnover and high order-to-trade ratios. Although there is no single definition of HFT, among its key attributes are highly sophisticated algorithms, specialized order types, co-location, very short-term investment horizons, and high cancellation rates for orders.
Among the major U. There are four key categories of HFT strategies: All portfolio-allocation decisions are made by computerized quantitative models. The success of computerized strategies is largely driven by their ability to simultaneously process volumes of information, something ordinary human traders cannot do. Market making involves placing a limit order to sell or offer above the current market price or a buy limit order or bid below the current price on a regular and continuous basis to capture the bid-ask spread.More...