Stocks slumped at Friday's open, as mixed earnings and weak economic data provided no lift for the market. The Nasdaq, S&P 500 and Dow Jones industrial average all shed 0.5% in early trade. Volume received a boost from options expirations, surging 56% on the Nasdaq and 126% on the NYSE, compared with Thursday morning's action. Industrial production slowed 0.4% in October, according to Federal Reserve data, down from a downwardly revised 0.2%