What's New -  August, 2005

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August 29, 2005:  A couple of small items to close out the month:

Minor problems in the Big Integers module occurred when invalid parameters were passed to Invmod or GCD functions.  Those are now handled.   Visit  Big Integer Test for more details and to download the corrected DFF Library module.

Viewer Mariano Lizarraga at  malife@gmail.com wrote to say that he has made a Spanish translation of the  Astronomy Demo  program  and would be willing to share it with any one who requests it.  Just send him an email request - mention whether you want source code or executable.  

August 26, 2005: 

I posted the "final" version of the Catapult Simulator today.  Results from testing against my new model catapult show reasonable agreement.   The differences between program results and real world results might be due to program bugs or real world model construction and measurement errors.  Only time will tell. 

August 25, 2005:  

I occasionally consult my Wordstuff program for a little help in solving  Mensa "Puzzle-A-Day" calendar problems.   This morning, I realized the version incorporating "Scrambled Pie" had never been posted.  So Wordstuff   now contains links to five word puzzle solvers.

Still working on the Catapult program.  The "update" posted on the 21st, actually broke more things than it fixed.   A previously corrected problem converting parameters between measurement systems was reintroduced.  It's fixed today, but I'm still having problems reconciling program results with real world results from my model catapult.  Like my "bullets" should be flying 5 times further than what I'm getting.   Either I'm measuring some parameters incorrectly or there's a problem with calculating the acceleration of the projectile when firing.   More later.         

August 21, 2005:   No, I haven't been on vacation again  as some surmised from the lack of  new postings this month.    I took a week or 10 days catching up on  Project Euler  problems in order to stay on the 1st page of rankings.  Also  tackled a couple of other projects. 

Newsletter #40 was published a week ago, so if you think you are subscribed but didn't get one, your mailbox may be full, an invalid address was submitted, an overzealous spam filter caught it, or some other problem prevented delivery.  There were only 30 or so of these this time and my File Update program made short work of deleting the invalid addresses from the mailing list.  

I spent a few days in the shop building a physical catapult  model to see if my Catapult program results agrees with Mother Nature's laws.  If not, I don't suppose she will admit to having made a mistake.   I did fire the first projectile today!  Tomorrow I'll replace the clamps holding it together with screws and get some measured results.    I did post a small revision to the program this afternoon to fix a problem causing  the projectile animation display taking a vertical jump between the firing and flight phases.   I expect to be making some more tweaks tomorrow when I get real world results.  

I also spent several days working on a generalized hull finding routine to fix a problem with the Tangram program which allowed invalid piece placement in some cases - program accepted pieces when vertices were inside the solution space, even though an edge passed outside (see image at left).  My idea was to identify the outside edges of the solution space and then check to see of the edges of the piece being placed intersected any outside edge of the solution.   

The hull finding program works but turned out not to be applicable to the Tangram problem.  I found tangram figures with holes and with disconnected parts that forced me to take another approach.   A fix based on checking for  piece edges with the background color on both sides was posted today.  

I may get around to posting the hull finder one of these days. 
       

August 5, 2005:  Here's program which solves sets of linear equations using a technique called Gaussian Elimination with Partial Pivoting.  Even the title sounds scary.  Fortunately,  this  demo program  is usable to those of us who are more results oriented and  don't worry about the messy details.  As usual, complete source code and other references are available for those  who do want to dig in.     

Oops!

August 3, 2005:  I spent the past two weeks working on our latest  program  - a Catapult Simulator.   Users define the mechanical characteristics of the catapult and the program predicts the flight time, height,  and range of the projectile.  Now I guess  I had better head down to the shop and finish that model to see if the program's output has any relationship to reality