@techreport{BallersteinMichaelsVigerske2013, author = {Martin Ballerstein and Dennis Michaels and Stefan Vigerske}, title = {Linear Underestimators for bivariate functions with a fixed convexity behavior}, institution = {ZIB}, address = {Takustr. 7, 14195 Berlin}, number = {13-02}, language = {eng}, year = {2013} }