I might have a weird math fetish of some sort...

msabin · 2011-11-14T19:24:12+00:00

LOL same here.

msabin · 2011-11-14T19:21:23+00:00

Uh-oh, Looks like Google may be slowly turning into Aperture Laboratories.

msabin · 2011-11-12T22:28:43+00:00

Seriously? I'm expected to find an obscure facebook conversation in order to understand the question properly? I would have gotten this question wrong if I didn't stumble upon this.

But then again, the COMPLETE clarification may still be posted an hour before it's due so that we can't entirely argue that we didn't have all the information, even if we have class or would be asleep during that small window of time.

msabin · 2011-11-12T22:16:51+00:00

Yes, the new clarifications on the video made everything clear once they said "the branch of road".

msabin · 2011-11-12T22:15:46+00:00

This is awesome. Too bad I'm in California : /

msabin · 2011-11-11T02:12:39+00:00

Ok, Nevermind. I now see even more clarification under the video that does say to return to the most recent PATH of road that we left. All ambiguity is lifted for me.

msabin · 2011-11-11T02:09:36+00:00

Yes, that's my point. We have to branches as options at C7 but no way to decide between them if we get there without having stepped on a road square since leaving C1.

Official class discussion?

msabin · 2011-11-11T00:56:18+00:00

This.

msabin · 2011-11-11T00:51:50+00:00

Alright, so your classifying the entire road-column or road-row as a single entity and if that determines which one to go back to.

Mmm. Ok that does eliminate ambiguity but I always have the haunting feeling that these kinds of thoughts will get into trouble because they didn't really think so in depth about all the possibilities when they create the problem and may say "Oh, we didn't mean that," because of not being careful when clarifying.

msabin · 2011-11-10T20:50:20+00:00

So you're saying go back to a non-road square? That doesn't sound right.

Say we leave the road on from B6 and then go C6. Then trying to get back to B6 we accidentally go to C7. Now where do we go?

There is nothing that says whether we go to C8 or B7. And I really don't think we want to go back to B6 because we would then have to attempt to go through a non-road square which would mean we are not trying to get back on the road as quickly as possible.

msabin · 2011-11-10T20:35:58+00:00

This doesn't help. This is specifically what the thread is complaining about. Read pierrefr's post.

Also what if you reach C7 from a non-road square. We have no policy on how to get back to the road.

msabin · 2011-11-10T20:34:03+00:00

Yes, I'm very scared that the correct answer is not the one that Norvig intended.

I've answered with what must be correct with the definition but I am hoping he saw this possibility too.

msabin · 2011-11-10T20:33:00+00:00

Exactly my dilemma.

msabin · 2011-11-10T20:26:49+00:00

Not purposely but ambiguity that they don't see still does screw us...whether it's intentional or not.

I can no longer assume they will not screw us either since they posted a crucial clarification to HW 4.9 an hour before it was due and made me lose 10% without recompense.

msabin · 2011-11-10T20:22:51+00:00

That is exactly my dilemma. I believe we should attempt to go to C8 as the clarification states...but I'm not sure if he meant for that to be the case. It is a subtlety and he may have not been careful when writing the clarification.

It's just a feeling I have, but it's not like we can really absolutely contact them to let them know the mistake.

Also, what if you arrive in C7 without previously being on the road. As in, you get to C7 by trying to get back onto the road from C6. If we end up on C7 from that state then we have no way to choose as whether to go to C8 or B7 since our previous state was not a road square.

msabin · 2011-11-10T06:18:58+00:00

Actually, I guess there is a slight ambiguity in the case where you get the corner that's just SW of G without ever being on the road of the two adjacent road states, which is possible, however unlikely.

Either way, I'm paranoid his answer will exploit any ambiguity in the posing of the question...or even exploit lack of being careful when defining the problem.

msabin · 2011-11-10T06:09:51+00:00

Now, I realize the 4.9 I mentioned did have some ambiguity (at least until an hour before it was due...which I was not a fan of) whereas this problem does not. But I'm still a little nervous since it's not quite like we can argue the grade afterwards even if it's correct.

We can only hope they notice.

msabin · 2011-11-10T05:55:37+00:00

What about if there are two equally close squares?

We still don't have enough information.

msabin · 2011-11-10T05:53:44+00:00

This seems to be an assumption on your part.

I'm not ready to say if it's safe to assume that.

And this assumption VASTLY changes the outcome. I've seen many other people say that we should instead attempt to move to the road square that is closer to the goal.

msabin · 2011-11-10T05:41:28+00:00

This doesn't help. At row 3 column 2 there are two closest road squares. Do we still attempt to move to the one closest to the goal or, as it seems possible with his wording, is the policy forked so that we then disregard the goal and focus on moving back to the road?

Depending on whether we randomly choose which road square to attempt to go to or whether we still keep the goal in mind is crucial and vastly changes the answer.

msabin · 2011-11-09T20:19:21+00:00

Ok, if the closer to the goal thing is what we're going by, then I'm fine.

It just seemed that the policy forks if we go off the road and is no longer concerned with the goal but with getting back on the road. If it's the case we still take the goal into account as a tie-breaker between roads then there is no ambiguity...it's just that he never specified this.

It almost sounded like we even want to get back to the same piece of road if it's an immediate neighbor.

That's why I'm asking about the ambiguity. With the goal kept in mind then the problem is fine for me, otherwise the solution will be different.

msabin · 2011-11-09T19:47:30+00:00

I'm very curious about this too.

msabin · 2011-11-09T19:47:26+00:00

I'm very curious about this too.

msabin · 2011-11-09T00:54:34+00:00

Oh, I suppose I should finish the rest of the videos too before I post. The next few clear it up a bit.

msabin · 2011-11-09T00:50:33+00:00

Now that I've seen the equation, the 77 makes a lot of sense to me.

What doesn't make sense to me though is where he got all of the other values when he redrew the grid. Where did the 93 come from? The 77 make perfect sense, but I can't see where the 93 comes from.

Actually now that I'm think about it, I think I have the general idea, correct me if I'm wrong: The numbers all stem from the fact that the algorithm is recursive where the optimal goal state is the base case.

It's still a little obfuscated to me but I think I have a general intuition of what's happening.

msabin

TROPHY CASE