Re: Generalised bisection

2009/3/16 Steven Tweed [off-list ref]:

On Sun, Mar 15, 2009 at 7:16 PM, Ealdwulf Wuffinga
[off-list ref] wrote:

quoted

On Fri, Mar 13, 2009 at 3:19 PM, Steven Tweed [off-list ref] wrote:
It is not obvious how to perform this algorithm incrementally, because
of the need to
marginalise out the fault rate. As I understand it, marginalisation
has to be done after you
have incorporated all your information into the model, which means we
can't use the
usual bayesian updating.

I had a look over the weekend, and got a bit sidetracked on one of
your assumptions. You seem to be assuming that the bug is such that
observing a single positive observation of the symptom at a position i
in the linear history _does not_ completely rule out that the guilty
commit occurs after that point. I would have thought the generally
more applicable assumption is that, given that generally you don't
have a bug ridden system where more than one bug causes the same
symptom _within the history of interest_, that a single observation of
the symptom does totally rule out the bug after that point (whilst
intermittency clearly not having observed the bug before that point
doesn't completely rule out the guilty commit being earlier, although
it should increase the liklihood estimate of the bug being later).

I think it's reasonable to expect false-positives as well as
false-negatives.  e.g. you're looking for a commit that slows down the
frame rate.  But on one of the good commits the hard disk hits a bad
sector and takes a bit longer to retrieve data and so you get a
false-positive.

It's a bit contrived, but I'm sure you can think of better example

John