# What's New - December 2000

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 December 19, 2000:  A couple of  demo programs are available for download from a new Math Topics article on Graph Searching.   The article describes the use of "depth first" and "breadth first"  searching for solutions of puzzles which can be represented as graphs.   SimpleSearch demonstrates the techniques with a trivial graph and CoinSearch finds solutions to the Sliding Coins puzzle.  A quick and dirty TicTacToe Count program is also included which generates all valid board configurations for tic-tac-toe (I think).  I get slightly over 6000 valid boards assuming X moves first.   If anyone can verify or correct this number, I'd appreciate it.   There was a show today on the History Channel about the Apollo 13 accident and what it took to get it safely back to earth.   One step was a precision "burn" of the rocket engines to get the ship to swing around the moon and slingshot back to earth.   That might make an interesting animated graphics Physics program.  Hmmm. We're off to my daughter's for Christmas, so postings are on hold for a week or so.   Here's wishing everyone a happy holiday season.      December 14, 2000:  Well, another 4-day Sabbatical has passed,  working on the  Sliding Coins puzzle this time.   Place 3 dimes and 2 quarters in a row like this        Then rearrange the coins to look like this     by sliding adjacent Quarter/Dime or Dime/Quarter pairs of coins  to a new location.  No reversing the order of the coins while dragging!  This is more of a program about drag drop processing than solution searching but worthwhile if you've never wrestled with drag images.    I also developed some good material on  searching  adjacency list representations of graphs.  I'll be posting  that in a day or two.   Note to H.R. Nazif.  I  have some information for you, but you forgot to include an email address in your feedback response.  Try again.   December 10, 2000: Two postings today.  Pi Calc #1 is a Beginners program that estimates Pi by shooting cannonballs randomly into a square field that just contains a round pond and counts how many of the total land in the pond.  Pi is the Greek letter p, our letter P, which they used as an abbreviation for perimeter.  Since Pi is the ratio of of the distance around a circle to the distance across, I guess it makes some sense.   No fancy graphics here - it  takes a million or so shots to get a good estimate, by which time the pond is full and  the field is pretty well buried in cannonballs. Spring Mass #1 is a new program introducing the physics of spring mass systems.  It animates the motion of a spring with a weight hanging from it when you give it a bump or stretch and release it.   About 300 lines of code puts it in the Intermediate category, but most of that is just setting up the data.  The animation loop has about 30 lines of code.  Would it work in zero gravity?  December 6, 2000:  BruteForce solves a class of problems with integer solutions.  As the name implies, it uses trial and error to search for solutions.  Word arithmetic problems, Magic Squares (well 3X3 and 4X4), and others like the Bookshelf Problem,  the Olympic Rings problem, and many others.  Check it out.