What's New -  May, 2009

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May 1, 2009:

  A week of algebra, geometry, and trigonometry refreshers was enough to convince me what I was already quite sure of, but had never proven, that parallel rays striking a parabolic surface are indeed all reflected to a common focal point.  Here is a Parabolic Reflections program which applies the math to see where it takes us.    The web page steps through the required math.  
 

May 2, 2009:  I decided last night that Parabolic Reflections posted yesterday should be able to display more information about  the intermediate steps in defining the reflected ray.   Parabolic Reflections Version 3.1  posted today corrects that deficiency.

May 7, 2009:   

 The objective of the Forbidden Connections Puzzle is to enter the digits 1 through 6 in the circles in this diagram in such a way that no number is connected to its adjacent value.  (For example, there can be no line connecting the "3" circle with the "2" circle or the "4" circle, etc.)  The program allows user play, finds the two valid solutions, and gives user hints if needed.   
 

May 12, 2009:  A housekeeping update today replaces DFF Library zipped file DFFLibV12 with DFFLibV13.  The library file contains a number of units which are used in multiple programs here on DFF.  Any of modified units methods included here reflect minor bug fixes or have already been included in source code of programs which required the enhancements .  Library units which are currently duplicated in program source code will be removed as those programs are updated, so no need for any immediate action by programmers.   The library zipped file file contains text file DFFVLib13.txt describing the changes in this version.    One program, Big IntegersTest, has also been reposted with new buttons to test the five new methods in our large integer class, TInteger, which resides in unit UBigIntsV3.

May 14, 2009: Oops - I changed everything in the DFF Library update except the actual file name in the download code.   I was clued by the fact that  the old version, DFFLibV12, was the downloaded 23 times yesterday.  If you were one, please try it again.      

May 19, 2009:

  Today's puzzle assignment, should you choose to accept it, is to rearrange the numbers 1 through 16  in a 4x4 grid so that the sum of any two adjacent numbers, horizontally or vertically, form a prime number.   (Prime numbers are positive integers divisible only by 1 and themselves.)   No credit given for the sample shown here. J  After you give up, program Prime Pair Sums will show you the other 2991 ways to do it.
 

May 27, 2009:  Summer is rapidly approaching and programming time is getting reduced by gardening, lawn mowing, grandchildren graduating (2 more from high school this year).   I decided to post a puzzle from my future projects file that I had written a year or so ago but never got around to document.   The problem is to find all 5 digit numbers that contain the same 5 digits when they are multiplied by 3.   Then,  coincidentally,  yesterday's Mensa Puzzle-A-Day calendar had another puzzle related to the number 3:   Find  all 3 digit numbers, N, which together with 2*N and 3*N contain the digits 1 through 9 exactly once. Today's Treble Puzzles posting solves both of these.