Wonderful sudoku test, congratulations for organizers and all toppers! Classic sudokus are my old complaint, but I think this time I chose the wrong tactics. I have the same number of performed puzzles as Jakub and Thomas, and look at the difference! I solved all matchmaker in about 85 minutes and the rest of time did only 6 classics.

Thanks to Lin Ming Fang.. very logical and definite clues to figure out the match makers :-)

To luckypunk: you can search "intersection, pairs, x-wing" by google.
To rakesh_rai: diagonal, touchy and no 3 odd/even in line are most difficult in variants part, both the puzzle itself and determining the rule. But if one solved as the order we show, he can complete at least 5/8.
Are there someone need help with the puzzles? Please let us know. All puzzles can be solved by logic.

yo thnxs min..got many links...will improve now..

MinFang Lin: If you could give a few starting steps on the diagonal (without trial/error), that'd be helpful. I am stuck at the beginning itself

Deb told me about this, maybe your question is many players' question.
i will show you later...please give me some time to do it.
Are there any other questions?

Thanks for this wonderful tournament, I've just finished to solve grids (I redo the entire relay as it was a catastroph during Test).

About my test:

I did wonderful stupid mistakes on part I (relay): Bad report of relay numbers between puzzle 1 and puzzle 2 (I lost about 10 minutes at the very beginning of the test ). On another relay puzzle, I copy numbers on cells with grey circles instead of cells with white circles .
After 1h10 and finally 7 relay puzzles laboriously finished, I begin "match maker part", it was fun and I manage to solve 5 grids in about 35 minutes (with one mistype - a single digit - on the antiknight), which is quite good, I think. Then during the last minutes I try to solve the last relay puzzle, with no success .

After the test, I finish "match maker part". It was really fun and very good grids. Diagonal was very tough, perhaps too much for this 2h tournament.

grids 17 were fun, too !

I think, inversely to "sampler platter", it was a little bit too difficult for a 2h tournament. Relay are always a trap because you can't do mistakes, otherwise it spreads on next puzzle and you are blocked on every other grids.
Perhaps a 6-grids relay and easier diagonal grid on match maker would have been more balanced for a 2h tournament.

However, it was a very good test with very good grids ! Thanks !

Fred

Transfer square No.16 (row 4, column 5 in the diaonal puzzle) has only possible digits 2,5,7. Look at final twin puzzle, transfer clues 1 and 14 are digits 7 and 2. So transfer clue 16 has to be 5 and transfer clue 15 is 8 (only possible 8 in irregular shape)

When you add these two digits, diagonal puzzle is easy to complete

Of course, this trick is possible only if you already solve some others matchmaker puzzles before diagonal.

Edited by Gotroch 2010-08-17 7:21 PM

there is much of a tie in the standings. Should they not be classified according to the time resolution?

Good point Fred. Not sure if we should change anything for this test, because we didn't annouce anything before the test. But in future we must introduce tie-breaker rules.

If others think that we should break the ties based on submission time, we can try to that for this test itself.

!

And with that post, this thread becomes the thread-with-most-posts at LMI forum

The first step of diagonal:

See D\ only two place can be 7 (r1c1 and r5c5), so r1c9 and r9c1 can't be 7.
Then check D/ only one cell can be 7, it's r5c5.

The technique is called crossover.
You can learn it from http://www.sudopedia.org/wiki/Crossover
or search it by google.
Any other question?

Thanks Min. After that crossover step, it does indeed solve out logically.

It will become easy buddy when you spend some time and give the total time till the submission of last answer in minutes instead of time of submission.....

I am happy to see others found the Diagonal to be difficult. I spent many minutes trying to find that first number and simply couldn't find it for quite some time! But once I did I was able to make some progress -- it still was not easy from that point forward however.

The crossover step is perfectly legitimate, and I think this is one of the best Diagonal puzzles I've ever solved. Like many others on the test, it is 5-star.

When it comes to ties -- I'm reminded of the 2009 Semifinals where a time-based tiebreaker for incomplete solutions was used, and it did not seem to work out very fairly. If two great solvers did exactly the same puzzles and didn't finish, maybe they both deserve the credit?

I was not in Zilina, but I think it's a very different situation. Here you have not to choose stop playing before end of time. You can submit answer before the end of test and continue to try to solve last puzzles.
if two great solver who didn't finish have same amount of points, but one reached it after 1h45 and the second after 1h58, it seems fair to me that the first one appears first in the ranking.
I don't say it's not fair now, it's just a detail, not very important for the LMI tests.

For diagonal sudoku, I've quite often found visualizing placements along the extra constraint, such as at WSC2 Prague Final and here, incredibly valuable. Indeed, so much so that I specifically take time in my solving routine to think about the immediate consequences of any number much more so than any other variant, kind of like a Nishio where you see if a few placements down the way you can possibly place all 9 instances of a digit with exactly 1 on each diagonal. This is generally not useful on classics, since a lot of either/or choices in empty space don't do much, but on diagonals the difference between two options is often digits on 0 diagonals, or 2 digits on a single diagonal, or other results that can't work. So I would not say I was looking for a crossover here (I'm not familiar with the term actually). But one of the first things I did was convince myself R1C1 couldn't be a 4. Similar thinking next showed me the 7 couldn't be in that spot either, so one or the other had to be in the center and that became obvious as the 7 (leaving R2C2 for the 4). That's just how my mind approaches diagonals. And I guess I suspected by then, since no Matchmaker could have any digits placed without identifying the extra constraint, that some cool diagonal cycle was certainly the way to start the puzzle here.

Re: Zilina and tiebreaking - the fundamental problem in Slovakia was not grading playoff puzzles along the way, as has been done by virtually all other WPC/WSC hosts in my time competing. Having 36 semifinalists in a single heat made this impractical, but that's a whole other discussion about good/bad planning decisions.

Within your scoring system, you have time-stamps for when a solver has submitted their last "correct" solution which makes it clear when, at a particular score, solvers have reached that point. Imagine a close test that has a grossly undervalued puzzle that is a particular stumper for many people. Maybe no one solves it, maybe someone does. But if 3-4 people are tied without just that puzzle, then the first to have everything but that one solved is a very fair tiebreaker to use. Here, Jakub and I are still pretty close to tied within 2 minutes (not a terribly meaningful amount of time to separate us, but I'd pip him out), but anything approaching a 10-15 minute separation case, as was the case in Zilina, would have let a large number of tied solvers be separated fairly. There, many solvers reached 3 of 4 puzzles done with 10+ minutes left to attempt the last stumper. Slower solvers who eventually reached 3 of 4 puzzles done with 2 minutes on the clock just said done and turned in their papers since they had no chance to finish the last puzzle. Since you'll know when solvers get to a particular score, its not a comparable situation.

As one of the most vocal critics of competition rules, I'd be completely satisfied with using the last submitted time as a sorting method with granularity at 1 minute levels pretty reasonable to view as a tie break.

Edited by motris 2010-08-18 4:02 AM

Using the timestamp of the final correct puzzle is certainly not an unfair way to break ties. I don't think anybody would have a claim that they deserved to be ranked higher *because* they didn't submit until after the other person.

But when there are still puzzles yet to be solved, there are other reasons why someone could be "ahead" (which is to say they solved all but one puzzle more quickly than anyone else). If you are done with *all* your puzzles (and you solved on paper), then you immediately submit them electronically. But if you have one puzzle left...maybe you spend as much time as you think you can on that puzzle? Maybe you leave five minutes at the end of the test to transfer your paper solutions over to the website, so while it seems like you just then solved the second-to-last puzzle, really you reached that point many minutes before and were just stuck.

If this tiebreaker were adopted, since players from all over the world value LMI tests as the top monthly sudoku competitions, they would naturally want to rank as high as possible. But I think that would mean they would go from paper-to-computer-to-paper-to-computer...over and over near the end of the testing period, which is just when they need to focus the most on solving. I think that's needlessly inefficient and doesn't really reflect who's better.

I would prefer weighting the puzzles themselves *slightly* differently. Give an extra 0.1 to the hardest puzzle, 0.01 to the second-hardest, 0.001 to the third-hardest...and so on. So if you match someone's point total, maybe these fractional points will provide the difference. Or, in the case where nobody finishes the test, let the top performers stay tied.

I'm in Zilina too. By the rule of round 2, i came to add-round, more than 70 players had same score with me. Maybe after that, many players use the rule to get previous rank. I think it's not fair to top players, maybe they only use 20 mins to finish 3/4, but the fourth puzzle is very very hard. Other players maybe use 30 mins to finish 3/4, if they submit first, they come to next round.
Online competition is different too, we can't know if one is still working on the puzzles after last submitting. If base on last submitting, it will be more unfair.
I had thought if it's necessary to make every variant in different points, as Ziti said, i can give diagonal 56 pts, and maybe non-consecutive 54 pts. But they are all 55 pts. Because it's unlike with classic, everyone will be good at different type of variants. If your are good at one variant but it has a low score, you will feel unfair to you. And see once again with the diagram, many players maybe didn't find P14 can't be no 3 odd/even, then diagonal, touchy, no 3 odd/even are last remain puzzles. As you see, the hardest step in diagonal is the first step, so i think one will give up this puzzle when he can't find any step.

Edited by Minfang Lin 2010-08-18 6:57 AM

To Thomas:
Do you know the technique Finned X-Wing, Empty Rectangle and ... they are alike nishio, and i think they are good and interesting techniques.

Every variant has its own special technique, and the designer should show it in his puzzle.

To Ziti and others (I'm sure you will like the logic ):
Find the next step of this diagonal sudoku:

(Hint: check digit 9)

Neeraj, Sorry it took longer than I thought I would take because of other commitments. But finally I've done it (2 weeks? after you suggested)

Updated score page - http://logicmastersindia.com/M201008S2/score.html

I've added 2 more columns -
LastCSub - stands for - last Correct Submission
TimeTillLCS - stands for - Time Taken till Last Correct Submission

Examples (for whom LastSub and LastCSub are different )
Gotroch : 6 minutes after he submitted the last correct puzzle, he just submitted P09 without filling anything.
Rohan Rao : 25 minutes after he submitted the last correct puzzle, he just submitted P09, which turned out to be wrong.

Many other examples are there. But I just choose top 2 for illustration.
The table is now sorted by Total Points Descending, then by TimeTillLCS Ascending.

However, I've not modified the Ranks yet, since players are having different opinion about using LastCSub as a tie-breaker rule.

I tend to agree with Ziti, when he mentions that paper players would be at a disadvantage since they might have to do paper-to-computer-to-paper-to-computer...over and over near the end of the testing period.

Lets wait for few more voices before we take a decision.

Very nice example Minfang. When I'm solving sudoku for fun I often run into eliminations like Finned X-Wing or Empty Rectangle which are very much what I'd just call situational thinking - like a Nishio with two steps ahead - but are pretty powerful to catch. When I'm solving classic sudoku for speed though, I rarely reach a stage where I'm searching for any of those things and on hard puzzles I will admittedly bifurcate with underlined digits to see if I can force a solution onto a grid. I'll also use uniqueness and other things that I wouldn't use when just solving logically.

To Ziti: Solving on paper versus online is a choice applied to all solvers evenly (choosing paper means you wait for it to print, but get the advantage of any notes you want, ...). Solvers can do some on paper and some online. Its the solver's option. So I don't think its necessarily unfair to apply a time-based standard that might require paper solvers to enter their answer with say 30 minutes left instead of at the last second, provided the value of time is made clear ahead of time. For this test, I entered all the relays and five of the matchmakers with ~25 minutes left, figuring I should get those pages entered, and then simply came back two more times to enter the last. Of course I missed one submit button (on the easiest respective "nonconsecutive" puzzle), but that's beside the point. I'd say you and others would use a similar strategy on the USPC - at some point after 2 hours make sure your answers are in place and then start trying to pick off 1 at a time. This approach - certainly with solvers knowing how tiebreaks apply - seems like one can adapt how they'd play on paper to not be disadvantaged.

Its also true that the matchmakers weren't evenly difficult, so changing their scores a little would help. More important is probably increasing the relative score of the matchmakers versus the classic relay as the classic relay was certainly a much higher point/minute value than the other which is why I started there. Solvers like Nikola that finished the whole Matchmaker were somewhat hurt scoring-wise by the relative valuation, although different scores for that section would certainly affect my strategy and likely others' as well.

Edited by motris 2010-08-18 9:06 AM