[TW-311] Estimated completion in burndown.daily shows impossible results

[taskwarrior]

Michele Santullo on 2013-10-25T10:44:42Z says:

In my case the burndown.daily estimates a project I'm working on will be completed on 20131110-1132 (that's 10th November 2013 at 11:32am).
The project in question only has one task left, however I realized the remaining task can't be really completed right now, so I did:
@32 modify until:20140115-0800 scheduled:20131220-2000 wait:20131215-2200@
That is, I don't want to see it anymore until the 15th of December, I will only be able to do that starting from the 20th of the same month and in any case it won't be doable after the 15th of January 2014. Out of curiosity, I watched the burndown.daily report again, and the estimated completion remained unchanged. Having told taskwarrior I won't even look at this task until one month past what it believes I will complete this task, that's clearly an impossible date. The day after the scheduled date, altough very unlikely, would be a better estimate, or to remain on the safe side, the "until" date would be good.

[taskwarrior]

Migrated metadata:

Created: 2013-10-25T10:44:42Z
Modified: 2015-11-07T20:54:09Z

[taskwarrior]

Paul Beckingham on 2013-11-01T22:07:47Z says:

Burndown completion date is an estimate based on the rate at which recent tasks have been completed. It does not take into consideration things like wait dates - it's simply the burndown rate.

I would prefer that burndown use a Monte Carlo simulation, like Evidence-Based Scheduling, but that requires a history of estimates and actual time spent on tasks. Even so, it would also not consider wait dates.

[taskwarrior]

Paul Beckingham on 2015-11-07T20:46:10Z says:

The algorithm used to estimate completion date has been replaced by something simpler and more robust: It is based on the net completion rate of tasks since the high water mark of total pending tasks, as measured on a daily basis.

So if the maximum was 100 pending tasks 5 days ago, and there are currently 90 tasks remaining, the estimate is (100 - 90) / 5 = 2 tasks/day, and 90 tasks at 2 tasks/day = 45 days

Note that the bug description refers to "impossible" dates, based on wait dates, assuming that Taskwarrior considers wait dates in the calculation. Taskwarrior bases the estimate only on the recent task completion rate, not user estimates.

A wait date is a forward-looking expectation, not hard data.