How does VirtECS® Scheduler Work?
APC has developed the Virtually Exhaustive Combinatorial System (VirtECS) to help manage resources over a time line. The VirtECS time line focus provides a highly goal-oriented way of organizing business data. VirtECS has capabilities to address the past, present, and future portions of the time line. To do so VirtECS needs information about process behavior and conditions. VirtECS can interact with process historians to query present process conditions and to compute statistical estimates of cycle times, yields and other basic performance data. VirtECS can also interact with Enterprise Resource Management systems to learn about present demands or network conditions and spreadsheets to register information about future scenarios that need to be investigated. In fact VirtECS has an extensive capability to acquire data from many different types of sources and publish results to many kinds of data repositories. VirtECS organizes this data using an XML-based Resource Task Network (RTN) language that intuitively describes process behavior.
VirtECS uses process data to generate a large set of mathematical relationships that incorporate process physics and to make predictions about future performance. As shown in Figure 2 some of the relationships have a “local” effect in that they enforce fundamental real-world behavior, e.g. conservation principles - material available now is equal to material available an instant ago plus whatever was produced minus whatever was consumed. Other relationships enforce constraints that occur over the entire future time line, such as the limited availability of labor or other resources. In fact VirtECS can very accurately represent behavior over the time line by using Very Large Scale Infinite Dimensional Programming (VLS-IDP) to divide time into infinitesimally small slices. The mathematical relationships are written over each small time slice to enforce real world constraints. VirtECS contains a highly sophisticated solution technology known as the Extensible Linear Integer Scheduling Engine (ELISE) for simultaneously generating and solving the mathematical relationships. In solving these relationships, ELISE uses business information to rate each and every future time line it examines to determine a very good or even best time line and the decision choices needed to realize it. The advantage of using a system of mathematical relationships is that ELISE can make a change at an earlier time that is quickly registered at all future times. As in the movie “Ground Hog Day”, the ELISE solver can quickly search many alternatives for a period of time to find the best strategy. No other existing technology has the facility to quickly investigate the huge number of alternative time lines.