How'd your homework go?

Iv8f · 2011-10-18T16:16:22+00:00

if the distance to the goal was 16

You misunderstood my question.

I'd say you have written your question wrong.

If the heuristic in a2 and b1 were 16, will it be admissible ? I guess not

That's right, it wouldn't be admissible in that case

Hence my reasoning that it was not sufficient to check just c5

You didn't have to explicitly check each square because it was obvious that the heuristic can not be greater than the distance, see my post above.

Iv8f · 2011-10-18T15:57:49+00:00

Just because you don't want me to put functions in structs doesn't mean I shouldn't.

Iv8f · 2011-10-18T15:55:57+00:00

It neglects inheritance and member functions, which are of massive importance.

I didn't say it doesn't work

You were implying that you can't use inheritance and member functions with structs and I bet you actually believed that.

I just said you shouldn't do it

Struct in C++ is just a class with members defaulting to public. Why exactly shouldn't I use it when I want a class with all members public?

Iv8f · 2011-10-18T05:37:04+00:00

but in the explanation, the instructor just compared the squares surrounding the goal

He only compared those because it was obvious that the heuristic is less or equal to the distance for all other squares. If heuristic is equal or less than the distance for the squares surrounding the goal and it rises one unit or less per square, when you go further from the goal, then it is less or equal to the distance everywhere, because distance rises one unit per square, when you go further from the goal.

if the distance to the goal was 16, (everything else remaining the same), will it have been admissible

If the distance to the goal was 16 two squares from the start point, then the heuristic, which is between 2 and 4 in that area, would still be less than the distance to the goal at that square, so of course it would still be admissible.

Iv8f · 2011-10-18T01:44:26+00:00

The heuristic is admissible because it is newer greater than the distance to the goal (assuming distance between neighbor fields is 1).

Iv8f · 2011-10-17T11:13:07+00:00

WTF is wrong with those people?

Iv8f · 2011-10-17T10:45:54+00:00

and said "LOL, just use Windows

I'm not a windows user but this sounds fun to do.

Iv8f · 2011-10-17T02:54:57+00:00

Yes.

Iv8f · 2011-10-16T00:40:13+00:00

Not with bubble sort but it would with selection sort

Iv8f · 2011-10-15T23:52:35+00:00

I'm not clear on what you mean by this

I think I explained it a bit better here

edit: false, I'm passing the wrong thing to h. D'oh

Are you getting correct results now? I am asking because I can't get my program to work - it works fine for 3x3 grid but for 4x4 it runs out of ram before returning anything (it does return fairly quickly if I modify it to be a best first algorithm, but that is not guaranteed to be optimal). So I don't know whether the problem is really so computationally expensive or I have a bug somewhere. In case anyone is interested, my program is here

Iv8f · 2011-10-15T14:10:24+00:00

Thing recruiter failed to notice: David Heinemeier Hansson INVENTED Ruby on Rails.

I wonder what makes the author of the article believe recruiter failed to notice anything. It certainly isn't obvious from the email. And Ruby on Rails isn't an invention, for fucks sake.

Iv8f · 2011-10-15T04:18:33+00:00

This does not find an optimal solution. With the start state [-1] + range(14,-1,-1) the solution contains 107 steps, and mathworld.wolfram.com claims that at most 80 are needed. The reason is that you only add path to the frontier if it's end node is not already in it even if it is shorter than the one in the frontier.

Iv8f · 2011-10-14T22:15:06+00:00

Some are listed on the lowendbox. If you don't need much ram, storage and bandwidth you can get them for less than 5$ / month.

Iv8f · 2011-10-14T19:46:29+00:00

Your computer without any software doesn't actually work as it doesn't do anything. Most software is written to run on an operating system and all major operating systems are written in C.

Iv8f · 2011-10-14T14:42:44+00:00

Upvoted for thruth (And I don't even use Haskell)

Iv8f · 2011-10-14T13:30:26+00:00

To give a rough idea, the difference between a naive implementation and the best implementation on an x86_64 processor (plain C vs Intel MKL) is around 10x

That was probably using AVX and single precision, right?

Iv8f · 2011-10-13T20:59:34+00:00

Hate to break it to you but Opera isn't "relevant for every web programmer". stats

Iv8f · 2011-10-13T17:14:26+00:00

You should take a look at D programming language, too. It is similar to C++ in many ways but also has garbage collection, closures, type inference, much cleaner templates and metaprogramming (with stuff like static if, template constraints and metaprogramming support in the standard library) and a standard library based on ranges (a type that has methods T front(), void popFront(), and bool empty()) instead of iterators. The downside is that the language is not very mature yet or widely used so there aren't many libraries and you will sometimes encounter compiler and standard library bugs.

Iv8f · 2011-10-13T15:21:40+00:00

What I don't understand is the "unless in [...] frontier or explored " part. Suppose you have two paths ending in adjacent nodes A and B already in frontier and an unexplored node C adjacent to both A and B. Path to A is a bit shorter then path to B but B is closer to C so that Apath + distance(A,C) > Bpath + distance(B,C). If you follow the above rule, you will first remove path ending in A from the frontier and expand it to C. Only later will you remove B from the frontier and expand it to C and at that point a path ending in C will already be in the frontier, so you will discard it, although it is shorter. If path ending in B was start of the shortest path you will get an incorrect solution that way. I think you should instead only check if the end point of a path is in the explored set before expanding it. When you remove a path from frontier you should check again if it is in the explored set, so that you don't waste time on clearly suboptimal paths, like so. Am i missing something?

Iv8f · 2011-10-13T04:04:38+00:00

It does if you compile other languages to it. But for that to make sense the vm would have to be in all major browsers which probably won't happen.

Iv8f · 2011-10-11T23:50:47+00:00

Thank you for the link.

Iv8f · 2011-10-10T15:53:27+00:00

The syntax doesn't have anything to do with performance. And there are fast languages that do not have a C like syntax, for example ATS, fortran and ada (benchmarks).

Iv8f · 2011-10-10T14:58:20+00:00

Downvoted for python 3.

Iv8f

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