Combinations

Combinations are complex possibilities for accomplishing one of the following tasks, without causing any conflicts:

• Schedule a single occurrence of an activity;
• Move an existing activity’s cell, or find swaps with other cells;
• Fill a gap (an empty cell) in a resource’s timetable;
• Find a suitable room for an already scheduled activity.

When we say "possibilities", we do not refer only to simple single-step actions (such as moving an activity from Monday to Tuesday, which can easily be done using drag-and-drop), but also to more complex multi-step operations involving several cells, ultimately achieving the desired result.

This is a very powerful feature of the program, and it can be incredibly helpful in "tight" scheduling scenarios. The program's ability to search through a vast range of possible moves can save a tremendous amount of time.

This is especially useful in schools where the final stages of timetable construction often take the longest. The reason is that, once most activities have already been scheduled, there are very few vacant cells left for the remaining activities — especially when resource allocation is close to full capacity. In such cases, "squeezing in" a new activity is far from trivial.

That is exactly where the combinations engine becomes an invaluable tool.

Note: Combinations are a feature of the Interactive mode. They take conflicts, sets, and activity properties such as length and span into account, and display all possible combinations accordingly. However, they do not consider constraints. Constraints are enforced only in the Automatic mode.

How to find combinations?

The search for combinations is triggered simply by clicking the Combinations tab at the bottom of the workspace. The type of combinations the program searches for depends on what you click on beforehand. The following options are available:

Scenario 1: Scheduling an Activity

When the Combinations pane is open and you click on an activity in the Activities list, the program searches for possible ways to schedule that activity. The results are displayed as thumbnails in the Combinations pane. When you move the mouse cursor over a combination thumbnail, the program displays arrows in the main timetable to illustrate the moves involved in that combination. The first arrow indicates where the selected activity will be scheduled. The following arrows show the moves required to relocate the conflicting activities.

Note that the first combinations displayed in the Combinations pane are usually simple one-step scheduling possibilities — for example, scheduling the activity on Monday, 1st period (provided that such direct possibilities exist). The following possibilities, however, become increasingly more complex. For example, a 2-step possibility may involve scheduling the activity on Tuesday, 2nd period, while moving a conflicting activity from Tuesday to Wednesday. The program searches for combinations containing up to 5 steps.

Scenario 2: Moving an Existing Cell

In this scenario, the goal is to move a specific scheduled cell to a different day or period. To trigger this combination search, simply click the cell. The program will then search for two types of possibilities:

1. Possibilities that move the cell to a different time, thereby freeing the original cell.
2. Possibilities that move the cell to a different time while also moving another activity into the original cell — such possibilities are called swaps.

In both cases, whenever a cell is moved instead of another cell, the program continues moving the affected cells in a chain until all cells are successfully rescheduled without causing any conflicts.

Note: If you want to find only moves or only swaps, you can use the selector at the top of the Combinations pane to filter out the irrelevant types of combinations.

Scenario 3: Filling a Gap

A gap is an empty cell — but not just any empty cell. A gap is an empty cell that has scheduled cells both before and after it. In many schools, it is desirable to minimize gaps in resources’ schedules. In this scenario, the combinations engine searches for ways to close such a gap by moving an activity that is scheduled at the end of the day. The reason for selecting activities from the end of the day is simple: moving an activity from the middle of the day would merely replace one gap with another, which is not the intended outcome.

To have the combinations engine search for ways to fill a gap, simply click the empty cell. As usual, the combinations found by the program will be displayed in the Combinations pane.

How to analyze the effect of a combination?

When you look at the arrows depicting the moves of a combination, you are usually seeing only part of the picture. This is because every activity that is moved affects all of the activity’s resources — not necessarily only the ones currently visible on screen. For example, while viewing the arrows inside a group timetable, you do not see the effect of the combination on the involved teachers. However, in order to properly assess the quality of a combination, you need to see its effect on the timetables of all involved resources. So how can you do that?

To do that, simply right-click the combination. A menu will appear showing all resources affected by it. When you select one of these resources, its timetable is displayed in the Timetable pane (in the bottom-right corner of the screen), together with the arrows of the selected combination. This allows you to assess the effect of the combination on the timetables of all involved resources.

How to apply a combination?

To apply a combination and have the program execute its moves, simply double-click its thumbnail, or right-click it and select Apply from the popup menu.

How to prevent specific cells from being moved?

By default, any cell may be involved in the move steps of a combination if the program determines that doing so is beneficial. However, it is possible to prevent specific cells from participating in any combination by fixating them. A fixated cell remains in place and is treated as non-movable by the combinations engine. To fixate a cell, select it and then choose Edit → Fixate either from the main menu or from the right-click menu.

A fixated cell is displayed with a small lock icon in its top-right corner.

Fixations are useful in situations in which there are constraints which the program is unaware of which prevent certain cells from being realistic candidates to participate in a combination. In these situations, you can fixate the relevant cells so that the program does not even suggest such unrealistic possibilities to you.

To remove a cell's fixation, select Edit → Unfixate in the main menu or in the right-click menu.

The next chapter: Automatic Timetabling.