????圍繞騎士資本公司（Knight Capital）和其造成4.40億美元損失的軟件故障一直有一個疑問：為什么身為美國首屈一指的造市商，處理全美超過10%股票交易的騎士會把一款容易出故障的軟件推向市場？

????騎士CEO托馬斯?喬伊斯在一次電視采訪中解釋稱，公司新的軟件程序向市場發出了數千錯誤交易，是源于“一個嚴重的程序錯誤”。上周三，騎士新的軟件程序與紐約證券交易所的新平臺同時上線，允許像騎士這樣的造市商給零售投資者提供略有折扣的股價。

????問題不在于騎士的離經叛道——過去15年，它的聲譽已得到改善。問題是，電腦程序員們稱，交易軟件永遠都做不到100%完美，特別是當一個新軟件推向像股票市場這樣復雜的系統時。主導當今股市的電子交易所具有的這一特性無疑將在未來引發更多的危機。

????“因為軟件有很多行代碼，很多變量，加之軟件應用所處的不同狀態，這個數字會極其龐大——數值可達10的100方，”卡耐基梅隆大學（Carnegie Mellon University）電氣和計算機工程系主任埃德?施萊辛格表示。他說，仔細核對行代碼不是不可能。數學定理可以進行測試。但不可能實現的一點是，評判一家公司的軟件——以騎士的軟件為例——將如何與數以千計的迅速流進和流出這個市場的其他算法相互作用。這只能在軟件實際運用時才會發生。

????施萊辛格對完美交易軟件的想法報以一笑。專家和政客們紛紛呼吁要對交易軟件實施更高的標準，倡導零錯誤代碼。對此，他回應稱這是不可能的。這就像要求橄欖球外接手能在每次對抗性防守訓練中都要接住橄欖球，否則就只能坐在替補席上。

????對于騎士而言，不幸的是過去15年來它賴以成功（這種成功推動了它的規模不斷增長）的因素上周釀成了巨虧。與其他發現問題就立即停止交易的高頻交易商不同，騎士這樣的造市商運用算法將來自Scottrade、先鋒公司（Vanguard）等不同客戶的買賣指令進行撮合，除非有重大錯誤出現，就必須接單。因此，他們在交易了數以千計的股票后才意識到了問題。

????“造市商需要一直留在市場中，”柏魯克學院（Baruch College）和紐約大學（New York University）斯特恩學院（Stern School）金融市場信息系統教授伯納德?丹尼弗表示。因此，市場波動對造市商的影響超出快速進出市場的高頻交易商。“如果我是其他人，我就可以這么說，‘嗯，讓我暫停一會交易，’”丹尼弗說。“他們沒有一家造市商的指令量。”

????丹尼弗說，監管機構不應追求完美的程序，而應當將重點放在程序算法失控時如何將損害降至最低：比方說，取消30分鐘時間窗口內的所有交易。實際上，這種觀點的背后是一些人呼吁在紐約證交所（New York Stock Exchange，簡稱NYSE）恢復人類造市商。人類的速度比電腦慢很多，更有可能在不正常現象升級至難以掌控之前發現苗頭。但回復到紐交所人類造市商排他、壟斷的交易模式，會讓二十年來的進展付之東流。這根本不可能發生。丹尼弗說：“如今，我們獲得了最低的買賣價差、最高的流動性和最快速的交易——對于大多數人，這是一個相當不錯的市場。”

????騎士這樣的造市商可能偶爾會出問題，交易可能不得不取消。但這就是當今高速電子市場必須付出的代價，對于大多數人來說，這樣的代價可能還算公平。

????譯者：早稻米

????One question keeps arising in the saga of Knight Capital and its $440 million software glitch: why did Knight, one of the premier U.S. market makers that handles more than 10% of total stock trading, introduce glitchy software into the market?

????CEO Thomas Joyce explained in a television interview that the company's new software program sent thousands of erroneous trades into the market because of "a large bug." This was software Knight introduced Wednesday in conjunction with the New York Stock Exchange's new platform that allows market makers like Knight (KCG) to offer slightly discounted stock prices to retail investors.

????The problem isn't that Knight is a renegade operator -- its reputation has improved over the past 15 years. The problem is that trading software can never be 100% perfect, say computer programmers, especially when it's new and introduced into a complex system like the stock market. That aspect of electronic trading, which dominates today's stock market, will certainly cause more crises in the near future.

????"Because it has so many lines of code and so many variables, the number of different states that software can be in can become [an] enormous number --10 to the 100th power," says Ed Schlesinger, head of Carnegie Mellon University's electrical and computer engineering department. Carefully reviewing lines of software code isn't impossible, he says. Math theorems can do the testing. What is impossible, though, is judging how one firm's software -- Knight's, for example -- will interact with the thousands of other algorithms rushing into and out of the market. That can only occur when the software is in actual use.

????Schlesinger chuckles at the notion of perfect trading software. Pundits and politicians have called for more stringent standards of trading programs, essentially advocating for bug-proof code. That, he responds, is impossible. It would be akin to sidelining a wide receiver until he catches every football in every practice against every opposing defensive scheme.

????Unfortunately for Knight, what made it so successful over the past 15 years -- its growing size -- worked against it this week. Unlike other high-frequency traders, who can flip the off-switch the instant they sense trouble, market makers like Knight, which use algorithms to match buyers and sellers from diverse clients such as Scottrade and Vanguard, are required to stay open for business unless there's a major error. They can trade thousands of shares before waking up to the problem.

????"Market makers are required to stay in the market," says Bernard Donefer, a professor of information systems in financial markets at Baruch College and New York University's Stern School. Volatility, therefore, affects market makers more than it does the high-frequency-traders whizzing in and out of stocks all day. "If I'm someone else, I can just say, 'Hmm, let me stop trading for a while,'" says Donefer. "They don't have nearly the amount of orders that a market maker does."

????Instead of pursuing perfect programs, Donefer says, regulators should focus on minimizing the damage when the program's algorithms go haywire; say, cancel all trades within a 30-minute window. In fact, that sentiment is behind the calls of some to reinstate human market makers on the New York Stock Exchange. Humans move much slower than computers, and are more likely to sniff out irregularities before they metastasize to unmanageable levels. But to revert to the clubby, monopolistic days of human NYSE market makers would be to throw away two decades of improvement. And it's simply not going to happen. "Right now, you got the lowest spreads, the most liquidity, the fastest trading -- it's a pretty good market for most people," says Donefer.

????Market makers like Knight may occasionally blow up, and trades may have to be cancelled. But that's the cost of today's high-speed electronic markets, and, for most people, it's probably a fair trade off.