Excel Add-in Development in C/C++: Applications in ... - F9

24 Excel Add-in Development in C/C++The dialog that appears is shown in Figure 2.2.Figure 2.2Excel’s Solver add-in dialogThis is a far more flexible solver, capable of solving for a number of inputs to get to thedesired single cell value, maximum or minimum. The user can also set constraints to avoidunwanted solutions and options that dictate the behaviour of the algorithm. Section 10.12Calibration, on page 381, talks more about this very powerful tool.The complexities governing when solutions converge, when they are unlikely to, whenthere may be multiple solutions, and to which one you are most likely to converge, arebeyond the scope of this book. (Excel provides help for the solver via the Tools/Solver...dialog’s Help button.) If you intend to rely on a solver for something important you eitherneed to know that your function is very well behaved or that you understand its behaviourwell enough to know when it will be reliable.2.11 EXCEL RECALCULATION LOGICThe first thing to say on this often very subtle and complex subject is that there is muchmore that can be said than is said here. This section attempts to provide some basic insightand a foundation for further reading.Excel recalculates by creating lists of cells which determine the order in which thingsshould be calculated. Excel constructs this by inspecting the formulae in cells to determinetheir precedents, establishing precedent/dependent relationships for all cells. Onceconstructed, cells in the lists thus generated are marked for recalculation whenever aprecedent cell has either changed or has itself been marked for recalculation. Once thisis done Excel recalculates these cells in the order determined by the list.After an edit to one or more formulae, lists may need to be reconstructed. However,most of the time edits are made to static cells that do not contain formulae and are nottherefore dependent on anything. This means that Excel does not usually have to do thiswork whenever there is new input.As this section shows, this system is not infallible. Care must be taken in certain circumstances,and certain practices should be avoided altogether. (VB code and spreadsheet