What's New - September, 2005
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September
29, 2005: I fixed a bug in
Brute Force today which surfaced while solving this division
problem. The solution requires letters be assigned digit
values 0 through 9 to make a true numeric expression.
Brute Force tries to solve sets of equations with integer values
by trial and error. A surprising range of puzzle types may
be solved this way, however, before today, equations with successive
minus signs were evaluated incorrectly. This puzzle and the
equations to solve it, were added to the included samples
as LongDivision.prb,
September 21, 2005: Note to AOL users. I am not able to respond to feedback requests from AOL email addresses. My replies get rejected with error "554 transaction failed". It seems to be a problem with AOL having excessively tight filters on senders and not being able or willing to correct the resulting problems. I spent several hours earlier this year, and my host site has also spent much time trying to correct the problem with AOL, but today's rejection indicates the problem still exists. (A Google search on "AOL 554 transaction failed" returns 19,000 hits, so it seems to be a common problem. ) I'm sure it is frustrating to those who send inquiries and not receive replies, and I know it is frustrating for me to spend time researching problems or questions and then having my response rejected. Fortunately, there don't seem to be many of you AOL types left.
To today's victim, AOL user Mike: Inverted text printing seems to work fine here. If you are using program TestMirroredText2.exe, let me know exactly what happens when you try to print. (Use a non-AOL email address please!)
September 19, 2005: From the "Computers as Tools" department, I wrote a little utility program today to Remove blank lines that saved several hours of error-prone manual editing. I added a new school to our Booksearch web but trying to update the index page hung MS FrontPage, my web editor. Investigation showed that 35,000 extra lines containing 10 blank characters each were scattered throughout the 136 valid HTML code lines! The normal 12Kb file now contained 360KB. What a mess! We may never know what hiccup caused this but the fix required about 25 lines of code and 15 minutes of "work" to create the tool and fix the file. I decided to post it to the Utilities section of DFF so I'll know where to find it in case the problem ever recurs.
September 14: 2005: A few years ago, I posted a Set Partitions program that addressed the ways that a set of distinct objects could be divided into separate piles. This week I finally had the need to explore the other kind of mathematical partition, Integer Partitions, which considers the number of ways that a positive integer can be written as the sum of smaller integers. 5 can be written a the sum of positive integers in 7 ways, for 60 the are about a million ways to do it! You can confirm for yourself such interesting properties as "the number of partitions of N into K parts is the same as the number of partitions whose largest part is K".
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Chaos - synchronized double pendulums after 30 seconds |
September 8, 2005: Mike Conlon was
writing a Basic program pendulum simulation recently and caught a
small math error buried deep in the double pendulum calculations
in our Pendulum program.
It doesn't make much difference in the apparent action of the
pendulum - just delayed the appearance of the chaos part of the
Chaos demo (two double pendulums, identical except for a 0.01%
difference in the lower bob weights , will start out synchronized
but soon behave entirely differently). Correction was posted
today/.
September 7, 2005: After several iterations, we are finally posting an update to the Big integers TInteger class which does large integer arithmetic. Viewer Charles Doumar has implemented a number of enhancements including a faster multiply and a new Nth root function. In addition several minor bugs and improvement in check input variable for validity were added.
Motivated by the need to test the changes in TInteger processing functions, I wrote a TRegress class which provides a framework for developing regression testing programs. Regression testing tries to catch is functions that are accidentally broken as other things are fixed or enhanced. In this instance TRegress helps build "Case files" with solved problems and runtimes from the old code and compares them with the same problems run against new code. It has proven itself quite helpful in testing the TInteger changes described above.