Rarely does a firm fire on all cylinders at once, but that’s how Zweig-DiMenna has produced some very enviable returns this year. The firm’s flagship Zweig-DiMenna Partners, an opportunistic global long/short equity fund, gained 4.33% in April, trouncing the Absolute Return U.S. Equity Index, which was up 1.77%. Year to date, the fund put up a net return of 18.44%, well ahead...