What's New - December, 2008

December 27, 2008: We are home from spending Christmas with our daughter and a few of the grandchildren. Besides being humiliated by a 4 year year in a "Pacman" competition, I have a grand assortment of new reading material which should last for the next several months.

I finished up and posted Monge's Circle Theorem demo program this morning illustrating that, given 3 circles, the three pairs of external circle to circle tangents do indeed intersect on the same straight line!

One last update before we take off to help Santa Claus with his deliveries. I ran across Monge's Circle Theorem the other day and decided to check out its surprising conclusion about pairs of tangents of 3 circles. Using the trusty "divide and conquer" problem solving technique, today's posting is Version 4 of our Geometry demo program which tests some new line and circle functions leading to the one to find the Circle-Circle exterior tangents needed for Monge. The demo includes brief descriptions of the algorithms used to construct the tangents.


1. Circle-circle intersection	2. Point-Circle Tangents (using circle-midpoint circle intersection)	3. Exterior Circle-Circle Tangents (using point-circle tangents)

December 12, 2008: One of the first programs posted when I started DFF 8 years ago solved the problem of finding the path from left to right through an array of numbers with the smallest (or largest ) sum. The original version used recursion, examining every possible path to find the largest and smallest. A sharp viewer recently pointed out that a much faster algorithm existed. Sure enough, Graph Traverse Version 2 posted today adds the new algorithm and solves problems in milliseconds instead of seconds.

December 8, 2008: Grandson Nathan, who's now 4, is into mazes During his visit over the Thanksgiving holiday, I generated some simple and some not-so-simple mazes for him using my Maze Generator Program. One was the "NATHAN" maze made up of the 6 letters connected into one long maze with a solution path over 600 rooms long. He hasn't solved it yet; in fact I discovered that rooms were too small when scaled onto a single printed page and it did not print very well across multiple pages. Version 3 posted today improves the printing and scrolling of large mazes. Grandma just pasted up and mailed him an 8 x 30 inch version!

I also added support for keyboard arrow keys in addition to mouse click/drag movement to trace out a solution path. Keys work better for 4-year olds!

December 5, 2008: Today I posted Version 3 of our CopyFolder program which copies all or selected mask files from one location to another. There's an option to replace files in the destination only if the source date is newer, but the date test was based on file creation dates. Today's update changes the test to use "Last modified date" which makes more sense in most cases. I also corrected a situation where the chosen destination folder was a subfolder of the source folder and the option was set to copy subfolder files. Oops - this set up a loop situation treating newly copied files as source files and copying them over (and over and over ...). A test now ignores the destination folder file when selecting files to copy.

December 3, 2008: A small change to the Intersecting Lines test program today. Version 3.1 fixes a problem where lines with large X values were not redrawn correctly. We now have 7 updates posted since the original version in 2001, probably more updates that any other program on the site. It's a good example of how competent our visual image processing system is compared to digital processing.

What's New - December, 2008

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