wabbit347 - Slashdot User

Submission + - Minimum number of clues required to crack Sudoku f (nature.com)

Submitted by ananyo on Saturday January 07, 2012 @07:22AM

ananyo writes: An Irish mathematician has used a complex algorithm and millions of hours of supercomputing time to solve an important open problem in the mathematics of Sudoku, the game popularized in Japan that involves filling in a 9X9 grid of squares with the numbers 1–9 according to certain rules.

Gary McGuire of University College Dublin shows in a proof posted online that the minimum number of clues — or starting digits — needed to complete a puzzle is 17; puzzles with 16 or fewer clues do not have a unique solution. Most newspaper puzzles have around 25 clues, with the difficulty of the puzzle decreasing as more clues are given.

Comment Re:Better Than Best (Score 1) 225

by wabbit347 on Tuesday September 28, 2010 @04:11PM (#33727652) Attached to: UK's Two Biggest ISPs Rip Up Net Neutrality

'Best Efforts' is a Quality of Service marking: usually Priority 1. It doesn't mean do your best at all costs, it just means do your best with the available resources. If a packet is received by a router that's acting on QoS markings that have a priority that's higher (eg Voice @ Priority 5) that should go through first. To use a car analogy; If you pay a premium (or buy a smart card or whatever) you can use special lanes or toll barriers to get onto the freeway faster. If you don't, you're lumped in with everyone else and have to make your best effort to get through the toll barrier. Disclaimer: This is fuzzy and half remembered from a CCNP course I did a couple of years ago. IANANE.

How To Build a Short Foucault Pendulum 79

Posted by kdawson on Friday February 13, 2009 @11:48AM from the watching-the-earth-rotate dept.

KentuckyFC writes "Set a pendulum in motion and you'll inevitably give it an ellipsoidal motion, which naturally tends to precess. That's bad news if you want to build a Foucault Pendulum, a bob attached to a long wire swinging in a vertical plane that appears to rotate as the Earth spins beneath it. The natural precession always tends to swamp the rotation due to the Earth's motion. There is a solution, however: the behavior of the ellipsoidal motion is inversely proportional to the pendulum's length. So the traditional answer has been to use a very long pendulum (Foucalt's original in Paris is 67 meters long). Now scientists at Carnegie Mellon University have another solution (abstract). They've created a motor that drives a pendulum in a way that always cancels out the precession. That means the effect of Earth's rotation can be seen on much shorter pendulums such as the 3-meter pendulum on which they've tested their motor. That's just the start though. They say there is no limit to how short the new generation of Foucault Pendulums can be, and even talk about the possibility of tabletop devices."

Slashdot Top Deals