Boom times have returned on Wall Street, at least for one trading desk. Goldman Sachs made $200 million in profit on a single day this February as calm in stock markets was shattered with a historic surge in volatility, according to people with knowledge of the move. That's on par with what the firm's derivatives unit typically makes in an entire year, said the people. The investment bank had positioned itself to benefit if the Cboe Volatility Index, the product sometimes called the "fear index" because it reflects expectations of future volatility, climbed, said the people, who declined to be identified speaking ... (full story)