The authors describe modular and flexible software developed for medium-term and short-term hydrothermal-generation scheduling. Both the medium-term and short-term programs model a wide range of system characteristics, including physical and operational constraints such as area interchange and reserve constraints. A matrix-generator generator (MGG) program is used to develop a matrix generator (MG) program for implementing the hydrothermal-scheduling problem formulation. The MG which is integrated with scheduling software, is developed so as to provide the capability for exercising different modeling options. A novel modeling approach is used for the medium-term program that divides the planning period into two parts with different time resolutions. This software has been used for operations planning studies for the hydrothermal system of Colombia in South America; these studies are used to exemplify the software's operations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>