German economic think-tank Deutsche Institut fuer Wirtschaftsforschung (DIW) is to raise its forecast for GDP growth for 2007 to around 1.7 pct, revised upwards from the 1.4 pct increase forecast in October, according to a pre-release of a report in Der Spiegel magazine. The DIW, which is due to publish its official forecast on Jan 3, declined to comment on the report.