 Citigroup Inc. lowered its stake in shares of PDF Solutions, Inc. NASDAQ:PDFS by 7.4 during the 4th quarter, HoldingsChannel.com reports. The fund owned 16,160 shares of the technology companys stock after selling 1,288 shares during the quarter. Citigroup Inc.s holdings in PDF Solutions were worth 273,000 as of its most recent SEC filing. Other hedge ... 