Schinckel.net

One program I tend to get around to writing in any new language I learn is a Sudoku solver. I originally wrote one in python, that solved every puzzle I could throw at it (although it had to guess and backtrack on failure in some cases).

Recently, I wrote one in Java. It was three classes plus a Driver/Main class. It took hours to write (at least the whole length of Phar Lap), and eventually it worked. I spent quite a while fixing up all of the syntactic errors I make in Java after programming in better languages again.

I then wrote one in Prolog. It was amazingly simple - it just defines a sudoku puzzle as a list of lists (each of which is 9 elements long), states that each element in each of the lists must be unique, and that each element in the first position of each list (columns) must be unique. Next, it states that each 3x3 grid must be unique, and that each element must be an integer of range 1-9.

That’s it. Solved.

My unique/1 predicate takes a list of items, and succeeds only if each item in the list is unique. This is simple:

1. An empty list is unique.
2. A list of one item is unique.
3. A list of the form [A,B|X] is unique if A and B are different, and [A|X] and [B|X] are also unique-lists.

I also use a predicate that indicates a variable should be of the value 1-9, it’s possible to use advanced techniques and something called “Domains”, but I couldn’t get this figured out.

The only trick then is in the definitions. The simplest to understand, but messiest is to define the elements in the sudoku puzzle as each having unique names ([[A1,A2,...,A9],[B1,...]] and so on), and then passing some lists to unique, ie all ‘Ax’ elements, all ‘X1’ elements, and so on.

The coolest thing about Prolog is that you don’t need to say how things will happen, but just what the desired outcomes are. This can be dangerous - it’s rather easy to write something that will be executed in a ridiculous amount of time, so you often need to think about how to narrow the search space as quickly as possible. In Java, I needed to have methods that would remove elements from a possibles list, and then check to see if there was only one element, in which case it’s the actual value that belongs there, and so on. This is all error-prone code, wheras Prolog’s backtracking does all of this for you.

The biggest benefit is that in a puzzle that is fiendishly hard, Prolog will still come up with a solution, wheras some other languages, using the algorithm I defined above may not. And, in Prolog, you will automatically get multiple solutions to a problem if they exist.

Can you tell I love Prolog?

Using Photographs to Enhance Videos of a Static Scene.

Wow.

Via Daring Fireball.

According to an item that just popped into my feed, there is now a version of Navicat that connects to Oracle DBs.

Cool. I like Navicat.

Heard on a TV ad just now:

Because the Olympics are filmed using Panasonic video technology, then it makes sense that you watch them on a Panasonic Plasma or LCD TV.

Clearly, someone at Panasonic can’t figure out that tricky logic stuff.

“Because you shit food out of your arse, it only makes sense that to eat it you should shove it up there too!”

I’m currently sitting in a café in King William Road, trying to get some coding done. I’m not achieving much, and there’s one simple reason.

There are a pair of absolute fuckwits sitting next to me, and they haven’t stopped talking for about an hour.

The guy, very gay, seems to be a drama teacher. If you are Australian, think of that show “Summer Heights High” - it’s Mr G. all over. I mean seriously.

The woman apparently has something to do with the arts - I haven’t been able to figure out exactly what skills she has, as whilst she’s been yapping non stop she hasn’t really said much of substance.

The last straw was when they were talking about some drama awards night, and she called it “wanky”. I was about to lean over and explain to her about irony - she hasn’t stopped wanking for about an hour!

Pretentious idiots annoy me. I’ll put up with snobbiness or aloofness in people who have real skills or talent. But these people are driving me nuts. I nearly bought my headphones, I so wish I had.

Aha! She’s a drama teacher too!

“It’s just like Pulteney Grammar all over again!”

I’ve never wanted Jaq to hurry up and pick me up from the café so much!

This is a post taken out of context I made to a discussion group in my AI subject. (Which another Matt and I have decided they falsely advertised, and should have called “Expert Systems”). It’s a bit vague in a couple of places, and I will probably come back to this topic at some stage and write a clearer explanation of what I mean. But this is here for now.

I did some thinking about the thought experiment where a guy sits in a room translating English into Chinese, and how “He will probably learn some characters over time.”, and how this is not the same as a machine.

I think it is the same. If a machine is able to recognise a word/character, that is still the same as the man learning it, rather than just memorising it. (I’d actually counter that memorising meanings and symbols is still a type of learning, and I come from an educational background, so I do know a little about learning).

But I want to push even further. A human isn’t the same as a translating program because it can learn new information that wasn’t there when the program was written. If a program is able to incorporate new facts, develop new pathways, and perhaps even rewrite it’s own program, then this is a much closer analogy to what we define is learning.

There are system out there that allow for dynamic reprogramming (I think some derivatives of Smalltalk are pretty good at this), and many systems that allow for dynamic alteration of code (perhaps by an outside source). Even the OLPC project is based on a system which can be changed while it is running.

Our brains are a machine that can alter it’s physical structure in response to the environment - indeed that is how we learn - and the pathways that are used often eventually end up working better than those that are used infrequently. A program could work the same way. Evolutionary programming is another example - an algorithm can be seeded, and then a variety of mutations are generated, and an “overseer” selects the mutations which result in a better algorithm.

I can’t provide any hard quotes, but I know this has been used to some extent to develop novel programs.

I know this is verging on Strong AI, which Darius says is a no-no, but consider this post as having taken place in a pub or cafe. In fact, I’m off to the pub now.

It’s still relatively unusual for me to have to work on a system that I don’t have superuser status on - at home I am the administrator of all of the machines, and at work I have sudo privs on both the development and production servers.

At Uni, however, I have to play by some other dude’s rules.

And, that means sometimes not having software installed that I need.

Take mercurial, for instance. I use this as my exclusive RCS, because it is simple to set up a repo, easy to clone, plays nice with OS X, and with Trac. It’s extensible, and easy to merge changes from clones.

But it isn’t installed as standard, or even at all on the Solaris machines at Uni. SVN is, but I’m not about to go through the whole rigamarole of setting up an svn server again. It just doesn’t do anything for me that mercurial doesn’t but it’s more setup work.

And I create new repos all of the time. I have one for each of my topics, and every time I start a new project, I create a new repository. It’s just that simple: hg init.

So, I tried installing it as a general user. I have it so that it works to some extent: I have the ability to change my environment variables, so I can add ~/bin to my path, stick all of the hg files in there, and then the mercurial/ directory into ~/.python, which I then make my PYTHONPATH.

Then, I can happily use hg while ssh’d in (or logged in to one of the SparcStation machines).

But, I can’t use the remote access.

See, ssh <machine> hg <command> will not work unless a) hg is in the system path, and b) mercurial is in the system python directory. You can fudge the first part (by explicitly telling the local hg where to look for the remote hg) but then I can’t figure out how to tell it where to load the python classes from.

So, my solution is this: mount the folder using sshd (or in my case, ExpanDrive). Then clone the repository from the local machine. You can then happily work away on either machine, but to push/pull you need to have the folder mounted.

Bit of a bummer. I’ve asked for mercurial to be installed, but we’ll see if that happens or not…

I have been searching for cheaper ways to buy textbooks (it’s crazy to pay $120 for a text, IMHO). I’ve chanced across www.textbookexchange.com.au. Let’s examine the workflow when trying to find a book there.

1. Visit the site.
2. Type in the name of the book or author.
3. Press “Search”
4. Be redirected to a login page.
5. Have to type in the name again because you were redirected back to the home page, rather than your search results.

I mean, seriously. It’s not that hard to keep some handle on state and redirect to the search results.

If I hadn’t saved so much money buying my books this way I wouldn’t use their stupid site!

As a class, we have the choice of what the focus of one of my topics this semester is going to be.

I’m voting for Compiler Construction. Even though we’ll be doing it in Java (ugh!), it is something I was disappointed to find wasn’t otherwise offered.

If you need convincing, read Stevey’s Blog Rants: Rich Programmer Food.

Now, if only I can convince the rest of the class!

First KP in ages today.

Tue Jul 29 13:50:14 2008
panic(cpu 0 caller 0x00192FD4): "pmap_flush_tlbs() timeout: " "cpu 1 failing to respond to interrupts, pmap=0x6b58ae0 cpus_to_signal=2"@/SourceCache/xnu/xnu-1228.5.20/osfmk/i386/pmap.c:4570
Backtrace, Format - Frame : Return Address (4 potential args on stack) 
0x628bfa18 : 0x12b0fa (0x4592a4 0x628bfa4c 0x133243 0x0) 
0x628bfa68 : 0x192fd4 (0x45f414 0x1 0x6b58ae0 0x2) 
0x628bfad8 : 0x1932b8 (0x6b58ae0 0x200000 0x0 0x0) 
0x628bfb88 : 0x195721 (0x6b58ae0 0x215000 0x0 0x14160a8) 
0x628bfbe8 : 0x169e6f (0x6b58ae0 0x215000 0x0 0x216000) 
0x628bfd08 : 0x16a437 (0x216000 0x0 0x0 0x0) 
0x628bfd48 : 0x182517 (0x1b32618 0x215000 0x0 0x216000) 
0x628bfd78 : 0x159209 (0x1b32618 0x215000 0x45 0x11d992) 
0x628bfdb8 : 0x12d17e (0x12a66d9c 0x874e0a0 0x0 0x0) 
0x628bfdf8 : 0x126257 (0x12a66d00 0x0 0x28 0x628bfee4) 
0x628bff08 : 0x1973dd (0x628bff44 0x0 0x0 0x0) 
0x628bffc8 : 0x19f3b3 (0x6b61820 0x0 0x1a20b5 0x12b56f20) 
No mapping exists for frame pointer
Backtrace terminated-invalid frame pointer 0xbffff508

BSD process name corresponding to current thread: configd

Doesn’t really give me much info, does it.