http://www.easyexcelsolutions.com/microsoft-excel-introduction/formulas-and-functions/ A formula is an expression which uses a calculation to define the value of a cell. A function is a pre-defined calculation that is readily available in Microsoft Excel.
Initial Boundary Value Problems in Mathematical Physics by Rolf Leis Based on the author's lectures at the University of Bonn in 1983–84, this book introduces classical scattering theory and the time-dependent theory of linear equations in mathematical physics. Topics include proof of the existence of wave operators, some special equations of mathematical physics, exterior boundary value problems, radiation conditions, and limiting absorption principles. 1986 edition.