On Wednesday, the S&P 500 stock index jumped 3 percent, as though all was right with the world. On Thursday, stocks collapsed, with the tech-heavy Nasdaq index plunging 5 percent as though the end of times was in sight.Things on Friday were only slightly better. The S&P fell again, but only by 0.6 percent, and the Nasdaq lost a mere 1.4 percent. It was the fifth consecutive weekly decline in the S&P 500, its longest streak of losses since June 2011.If you are looking for patterns in the market’s wild swings, the answer is simple: The financial markets are coming to grips with a stunning policy change by the Federal Reserve.Over the last two decades, financial markets may have become so accustomed to encouragement from the Fed that they just don’t know how to react, now that the central bank is doing its best to slow down the economy.But the Fed’s intentions are evident, if you read and listen.Jerome H. Powell, the Fed chair, said unequivocally during a news conference on Wednesday that the central bank was really and …
