Need to understand FET generation process

[Chafik Graiguer]

The most mysterious moments for me is when FET is generating tiemtable

There is some less documented points
When generator is runningة there are tree interesting buttons
- See initial order of placing...
- See difficult activities
- Stop and see impossible activities
What deos mean the initial order? and how it is important to know in order to diagnonse a difficult timetable?
The contextual help says:

This is the initial evaluation order of activities computed by FET. If the generation gets stuck after a certain number of activities, please check the activity corresponding to this number+1. You might find errors in your input

My timetable has 435 activities to be placed
let us consider the following scenario, which really happened to me this year
I started generation,
After 6 muinutes, FEt reaches 434 out of 435
Then fall back, start oscillating between 400 and 420 for one hour
If I look at initial order, I found at bottom list the most easy activities: Gymnastics activities, two hours per week, without any room constraint
I nedd to know, at the moment when FET fall back to 400, deos it mean first 399 actviities initially placed never get displaced, are still placed and that FET is only displacing and swapping the last 35 activities in the initial order list?

Now, suppose I click
See difficult activities
at 402 activities
Contextual help says:

Information relating difficult to schedule activities:
Please check the constraints related to the last activities in the list below, which might be difficult to schedule:
Here are the placed activities which lead to a difficulty, in order from the first one to the last (the last one FET failed to schedule and the last ones are difficult):

suppose the last actvities in the list is Id 301
but if I stopped it  at 410, it prensents me with another activity/activities at list bottom
If I stopped it at 415..etc
So at different moments , we have different difficult activities
which activity is really difficult?

Finally, what is differences between informations obtained from
- See difficult activities button
and from
- Stop and see impossible activities button ?

[Liviu Lalescu]

What deos mean the initial order? and how it is important to know in order to diagnonse a difficult timetable?

Initial order in which FET places activities. If FET reaches 434 activities, then trying to place activity number 435 in this list was impossible. The 434 activities could be placed correctly to respect all constrains, only this last one was too much.

My timetable has 435 activities to be placed
let us consider the following scenario, which really happened to me this year
I started generation,
After 6 muinutes, FEt reaches 434 out of 435
Then fall back, start oscillating between 400 and 420 for one hour
If I look at initial order, I found at bottom list the most easy activities: Gymnastics activities, two hours per week, without any room constraint

The last activities are indeed the easiest, but they might be too difficult to add, because the timetable is already full.

I nedd to know, at the moment when FET fall back to 400, deos it mean first 399 actviities initially placed never get displaced, are still placed and that FET is only displacing and swapping the last 35 activities in the initial order list?

Wrong. FET tries to put an activity, displaces others, maybe even the first placed activity. At least this is what I remember (I didn't check the allocation algorithm for a long time). But you can test this, copy/paste the information and compare by content with initial order of activities or with other stage.

Now, suppose I click
See difficult activities
at 402 activities
Contextual help says:

Information relating difficult to schedule activities:
Please check the constraints related to the last activities in the list below, which might be difficult to schedule:
Here are the placed activities which lead to a difficulty, in order from the first one to the last (the last one FET failed to schedule and the last ones are difficult):

suppose the last actvities in the list is Id 301
but if I stopped it  at 410, it prensents me with another activity/activities at list bottom
If I stopped it at 415..etc
So at different moments , we have different difficult activities
which activity is really difficult?

The difficult activities are the last ones, with which FET struggles and just allocated, and the last one which FET cannot allocate. But if FET cannot allocate, then FET puts it at a slot and gets out other activities, which will be placed after this, following in this temporary order.

Finally, what is differences between informations obtained from
- See difficult activities button
and from
- Stop and see impossible activities button ?

See difficult activities and stop and see impossible buttons are similar. But stop stops generation and also gives you a problematic activity, which is n+1 referring to maximum placed activities.