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Showing posts from May 23, 2010

geometric designs thru crop circle

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Perm url with updates: http://xahlee.org/crop_circles/crop_circle_1.htmlGeometric Design thru Crop CircleXah Lee, 2010-05-28Crop circles started as a prank, but now has become a medium for geometric designs. Here are some example of beautiful ones.Crop circle at Diessenhofen, Thurgau, Switzerland. 2008-07-15. Source Source This pattern is based on circles on a triangular grid. Such design is called flower of life. Source soulsofdistortion.nl 2007-08-01. Sugar Hill, Aldbourne, Wiltshire UK. Photo: Steve Alexander. Source 2008-07-27. Photo: Steve Alexander. Source Tidcome Down, Wiltshire, UK. Photo by Steve Alexander. Source For high school students, you can learn geometry by trying to duplicate these designs on paper. You can use the computer software GeoGebra to draw them interactively. Most crop circle designs are geometrically simple, so that you should be able to look at it, and figure out exactly the center and radius of each circle or triangle or other key points. You'll learn a…

emacs isearch of current word

Perm url with updates: http://xahlee.org/emacs/modernization_isearch.htmlEmacs Incremental Search SuggestionsXah Lee, 2010-05-29This page document a problem with emacs's incremental search feature, with suggested solution.Emacs's isearch has some problems. Suppose you have this line: the delete-current-file is quite useful to me. and your cursor is on the second dash. You want to search the next occurance of the word “delete-current-file”. You have to first move your cursor to the beginning of the word, then press a key for isearch, then another key to select “delete”, another to extend selection to “current”, another to “file”, then press isearch again to find the next occurrence. That's 7 operations. In GNU emacs, it's “M-b M-b C-s C-w C-w C-w C-s”. In vim, it's just a single key press.highlight-symbol minor modeToday i found several solutinos to this. I think one of the best is the package highlight-symbol by Nikolaj Schumacher, at: nschum.de highlight-symbol.No…

math decorative patterns on a sphere

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Perm url with updates: http://xahlee.org/math/decorative_pattern_on_sphere.htmlDecorative Pattern on SphereXah Lee, 2010-05-26Sphere with two-point pattern. “A two-point spherical Islamic star pattern with nine-pointed and ten-pointed stars. Created using custom-designed software, with a tiny bit of postprocessing in Rhino.” photo source This is created by Craig S Kaplan, a expert of mathematical decorative patterns.You can actually buy this, as a real object. $13 USD. Place it on your desk or coffee table, sure to attract admirers. Buy it at shapeways.com.For some interesting read, see: Islamic Star Patterns in Absolute Geometry (2004-04) By Craig S Kaplan, David H Salesin. ACM Transactions on Graphics 23(2):97-119, April 2004. SourceSpheres and Cubes StudyStereographic ProjectionAlgorithmic Mathematical Art

spiral in nature; violin scroll

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The neck of a unfinished violin. Source. For more, see: Spirals in Nature.

new version of ErgoEmacs keybinding

A new version of ErgoEmacs Keybindings is out. Version 5.3.3, released on 2010-05-27. Major new features are:Ctrl+p now asks for confirmation before printingCopy and Cut to will copy/cut current line if there's no text selection.Support for UK layout.Support for UK Dvorak layout.You can now change keybindings, e.g. if it conflict with other minor modes.Full detail is in the version history file in the package.Download at: ErgoEmacs Keybinding.

Emacs Spell Checker Problems

Perm url with updates: http://xahlee.org/emacs/emacs_spell_checker_problems.htmlEmacs Spell Checker ProblemsXah Lee, 2010-05-25This page discuss emacs's spell checking feature, its problems, and some practical tips.flyspell-mode ProblemsEmacs has a spell checking feature (flyspell-mode), that check spelling errors while you type, much like all other modern editors, word processors, email programs, or text box in browsers. However, emacs's spell checking feature is much worse than the spell checker in browsers or any commercial editor.When you have flyspell-mode on, it slows down your editing noticeably. Normally, when you hold down “Ctrl+→” (forward-word), the cursor moves fast across lines to the place you want. But with flyspell on, the cursor freezes, and when you release the key, the cursor shows in some other place. Essentially, the screen is not updated so often. This is just not workable.Another problem is that if you open a document, with flyspell-mode on, it does not …

Unicode BOM Byte Order Mark

Perm url with updates: http://xahlee.org/comp/unicode_BOM_byte_orde_mark.htmlUnicode BOM Byte Order MarkXah Lee, 2008-12-18, 2010-05-25Some notes on unicode's Byte Order Mark. Quote from Wikipedia:The byte order mark (BOM) is a Unicode character used to signal the endianness (byte order) of a text file or stream. Its code point is U+FEFF. BOM use is optional, and, if used, should appear at the start of the text stream. Beyond its specific use as a byte-order indicator, the BOM character may also indicate which of the several Unicode representations the text is encoded in.[1]Because Unicode can be encoded as 16-bit or 32-bit integers, a computer receiving Unicode text from arbitrary sources needs to know which byte order the integers are encoded in. The BOM gives the producer of the text a way to describe the text stream's endianness to the consumer of the text without requiring some contract or metadata outside of the text stream itself. Once the receiving computer has consum…

Second Life XstreetSL Item Disappears

Perm url with updates: http://xahlee.org/sl/xstreetsl_item_disappears.htmlXstreetSL Item DisappearsGet your Xah Particle Maker today! There's a really bad bug in XstreetSL. If you item has multiple languages, and when you edit the page or add a language, the item will disappear, for about 2 to 3 days.This is now a known issue, as jira bug 114.Here's some detail of my story.This happen to me too. I make slightly over $100 usd per month, and the primary product that made this happen is a particle making machine.My item is this xstreetsl.com ItemID 1387599.It does have multiple languages which i added long ago.On 2010-05-20, i tried to update the description for a new manual, and bang, the item disappeared. I went into panic. Spend 2 hours eventually found a place to post to Linden Labs support, and also posted to xstreet market place forum. Just got a notice from support today (2010-05-24) that points me to this jira bug page.It'd very bad for me particularly because i have h…

Martin Gardner (1914-2010)

Perm url with updates: http://xahlee.org/math/Martin_Gardner.htmlMartin Gardner (1914-2010)Xah Lee, 2010-05-23Martin Gardner died yesterday, at age 95 (1914-2010). He is the one who started me on the path of math. From about 1990 to 1995, i read pretty much all of his recreational math books (collection of his Scientific American column), as well as several of his pseudo-science debunking books. It is him, that made me decided that math is my career. (which turned into programing)Conway's Game of LifeOf his recreational math articles, the one subject i think that taught me the most is his intro to Conway's Game of Life (GoL). It introduced to me, back then a shocking idea, that deterministic behavior does not imply predictability. (in the 1990s, chaos theory, and computer drawing of fractals, run rampant as pop science. It was even highlighted in Hollywood movies such as Jurassic Park.) I've spent months playing the Game Of Life in 1990s, and every few years i'd re-vi…

AjaxLife, a web browser based Second Life viewer

Perm url with updates: http://xahlee.org/sl/blog.htmlThe emerald guys are announcing AjaxLife, a web browser based, text-only, Second Life viewer. So, if you are on a lousy computer with no graphics card and just want to login to chat with your friends or get your IMs, that seems a good solution. Start using here: http://ajaxlife-0.modularsystems.sl/.It works. Pretty neat.