Solver Constraints

There are miscellaneous options to ignore some constraints that are normally used or add additional constraints to give more flexibility finding a (feasible) schedule.

Network-related constraints are constraints owned by batches that were NOT selected themselves, but are connected by flows to the batch-selection. In many cases, the current position of these batches will constrain the position of the selected batches. Because limiting the degrees of freedom of the selected batches may not be desirable, it is possible to ignore the properties of these connected batches.

• Enabling Batches

  If this option is selected, the searched solution must satisfy these requirements:

  • The constraints for the process batches, the tank batches, and the enabling batches
  • The allocated resources for these batches

  If this option is cleared, the allocation of the enabling batches to resources and in time is not taken in account during the search.

• Utilities

  If this option is selected, the searched solution must satisfy the availability constraints of all critical utilities at all moments. The requirements must always respect the minimal and maximal capacity of the utilities.

  If this option is cleared, these constraints are not taken into account during the search.

• Inventory Constraint

  If this option is selected, the constraints that originate from inventory points are ignored.

• Ignore Resource Availability

  If this option is selected, availability on all resources for all selected batches is ignored. The availability is defined by timetables, time periods, and availability exceptions; but notice that the resource's occupation, as defined by batches and downtime is still taken into account. This option is useful when a schedule is very tight and almost fits - but not exactly - within the availability profile.

• Ignore Time Constraints Related Network

  If this option is selected, related network batches are NOT fixed in time. As a result, flows into or out of the selected batches are not bound in time. Hence, the selected batches have more freedom in horizontal direction. This is useful when the user's primary concern is not the related network, except for its routing constraints.

• Ignore Routing Constraints Related Network

  If this option is selected, related network batches are NOT allocated to their current resource. As a result, flows into or out of the selected batches can be routed more freely. Hence, the selected batches have more freedom in vertical direction. This is useful when you suspect a routing problem prevents the solver from finding a feasible schedule.

• Allocate Equal Products to Same Resource

  If this option is selected, the solver tries to schedule all batches with the same product on a separate resource. This works best if the number of products in the selection does not exceed the number of available resources in the choice group. In many cases, this option is a useful rule-of-thumb to minimize changeovers.

• Cycle

  Select this option if you want to keep a batch within its current cycle and limit how much the Solver can move a batch. The list next to this option contains all user-defined cycles. The Cycle option is disabled if no cycles are defined. The Cycle list and the Always Keep Within Cycle option are disabled when the Cycle option is cleared or disabled.

• Automatically Relax Constraints

  If this option is selected, the solver will automatically relax the constraints in a predefined order, when a partial or no feasible solution is found during the search.

  The order in which the constraints relaxed are:

  ASAP	JIT
  Batch not before fixed time constraint	Batch not after fixed time constraint
  Batch not before current start time constraint	Batch not after current end time constraint
  Batch not before first batch constraint	Batch not after last batch constraint
  Batch not before earliest start time	Batch not after latest end time
  Batch not before start of work area constraint	Batch not after end of work area constraint
  Inventory constraint	Inventory constraint
  Utilities constraint	Utilities constraint
  Enabling batches constraint	Enabling batches constraint