The U.S. stock market turned positive shortly after the opening bell on Friday but was on track to post its biggest weekly drop in five weeks. Equities were under pressure earlier in the week, as oil prices continued to fall and the shocking move from Swiss National Bank on Thursday rocked markets. The S&P 500 SPX, +0.08% was up 7 points, or 0.4%, at 1,999. The Dow Jones Industrial Average DJIA, -0.09% gained 45 points, or 0.3%, to 17,364 at the open. The Nasdaq Composite COMP, +0.14% began the day up 17 points, or 0.4%, at 4,586.