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Showing posts from June 20, 2010

Celtic Knots, Truchet tiles, Combinatorial Patterns

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Perm url with updates: http://xahlee.org/math/Truchet_tiles.htmlCeltic Knots, Truchet tiles, Combinatorial PatternsXah Lee, 2010-06-25A image made by Henry Segerman. This is made by using a “Celtic Knot font” (from clanbadge.com).Basically, this method is just a combination of square tiles. Each tile has a pattern. When 2 tiles are placed together, the pattern on them connect at the edges. When a bunch of these tiles are placed together, each tile may have different pattern or orientation, they form various knots or paths. If each tile's pattern and orientation is choosen carefully, a symmetric over all design can be created.This way of creating patterns is known as Truchet tiles.It can be done with equilateral triangles too, or, any tiling of n polygonal prototiles. Just make sure that the patterns on each tile is such that their edge can connect smoothly.For several tiles by the truchet tile method, see: Truchet tiles. Floor by Colin Fizgig, tube by Sleeves Rhode. These are cre…

How to Use Unison for Syncing Files (Unison tutorial)

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Perm url with updates: http://xahlee.org/UnixResource_dir/unison_file_sync.htmlHow to Use Unison for Syncing Files (Unison tutorial)Xah Lee, 2007-03, 2010-06-25This page gives you some practical tips on using Unison for syncing files on a local machine and a remote server. (or 2 directories on the same machine) Unison lets you sync files in both directions. The “rsync” tool does just one way sync. (It overwrites any changes on the destination machine) The “unison” asks you which direction you want to overwrite for each difference in file/dir.For brief into and history, see Wikipedia Unison. Unison home page is at: www.cis.upenn.edu unison.Both machines must have unison installed.Type “unison -help” for list of options.Type “unison -doc topics” for tutorial on different topics.Unison version must be the same on both machines. Type: unison -version to find out what version you are running.Usually, you install multiple versions of Unison on the same machine.To start with a particular vers…

Emacs Form Feed (^L) Display Suggestion and Tips

Perm url with updates: http://xahlee.org/emacs/modernization_formfeed.htmlEmacs Form Feed (^L) Display Suggestion and TipsXah Lee, 2010-06-24This page discusses some problems involving the Form feed character (^L) in emacs, and gives you some tips for better solution.In emacs lisp source code, sometimes you'll see “^L”. That's the “form feed” character, ascii 12. For example, type “Alt+x describe-function”, then dired, then click on the “dired.el” link to view the source code. Scroll around and you'll see it.ProblemThe form feed char is used in 1990s or earlier to cause printer to start with a new page. Printers today no longer use that in their protocol. However, sometimes it is also used by programer as a section marker. Many emacs lisp source code still have it. It is also sometimes seen in Python source code.The displaying of ^L is hard to read, and is mysterious to modern programers.SolutionYou can make emacs display a horizontal line instead. You need to install Pr…

emacs switching to Scheme

Perm url with updates: http://xahlee.org/UnixResource_dir/writ/emacs_switch_to_scheme.htmlEmacs Switching to Guile Scheme Lisp?Xah Lee, 2010-06-23Recently, there's discussion on Emacs dev forum about switching to Guile, a Scheme lisp. Of course, such discussion always sparks controversy. Namely, the Common Lisp camp isn't happy. Among the posts in the emacs dev list, those by Thomas Lord has some good info of emacs and Guile history around late 1990s. See: emacs dev. 2010-04-11, Thomas Lord.Here's the post that the Guile's current maintainer, offers his help on this and why he thinks it's a good choice. emacs dev. 2010-04-14, Andy Wingo.Whisper to myself: please don't fuck up, please don't fuck up.I hope the emacs maintainers would just let Andy do his work. In non commercially backup open source projects (e.g. not Google, Firefox), there's always huge number of opinions, ideologies, arguing and arguing for years, nothing gets done. What actually hap…

a Mathematica book citing my article

Perm url with updates: http://xahlee.org/comp/blog.htmlDiscovered a new book that cites my site. The book is:Mathematica Cookbook (2010), by Sal Mangano. amazon.The citation is: The Concepts and Confusions of Prefix, Infix, Postfix and Fully Nested Notations.For more, see: Printed references to XahLee.org and XahLee.org Site Awards and Recognitions.

emacs byte compile incompability on 23.1 vs 23.2

Perm url with updates: http://xahlee.org/emacs/elisp_byte_compile_problem.htmlEmacs byte compile incompability on 23.1 vs 23.2Xah Lee, 2010-06-22Stung by a emacs byte-compile problem. Cost: 2 hours.Summary: if you are doing elisp dev on more than one machine, best to re-byte-compile the files on the machine if you run into some strange errors.Byte compiled elisp files should work cross-platform for emacs 23.2. It has been working between my Windows Vista and Mac 10.4.x in the past year. Today, i just byte compiled the whole dir of elisp files on our ErgoEmacs source trunk, then synced over to my Mac as a regular routine, then started emacs on my Mac. I keep getting this strange error on my Mac: Wrong number of arguments: called-interactively-p, 1 Very odd error. Starting emacs with “--debug-init” didn't help. Turning on toggle-debug-on-error while emacs is running didn't help much neither.I thought some new change i made to ErgoEmacs recently caused the error. So, i started t…

emacs. new version of bbcode and unicode browser modes.

A new version of bbcode-mode.Also a new version of xub Unicode Browser mode.

Petronas towers

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Perm url with updates: http://xahlee.org/dinju/Petronas_towers.htmlPetronas towersPetronas Towers. A incredibly beautiful skyscraper, modeled in the style of ancient South Asia temples.Source Source Have a look at Khajuraho Temple, which is a ancient temple in India. You can see the similarity of the style.Architecture Beauties

xub Unicode Browser mode for Emacs

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Perm url with updates: http://xahlee.org/emacs/unicode-browser.htmlEmacs Unicode Browser: xub-modeXah Lee, 2010-06-20, ..., 2010-12-20This is the home page for xub-mode, a Emacs major mode for browsing unicode characters.Current version is 1.1.4, 2010-12-20Usage and FeaturesTo start the mode, type 【Alt+x xub-mode】.When this mode is on, pressing the arrow keys will display info about the character under cursor. Pressing mouse left button on a character also works.xub-mode in action. (this is a older screenshot. The zoom in/out keys have changed.) Press 【Ctrl++】 to zoom in. 【Ctrl+-】 to zoom out. Or, you can hold down Ctrl and scroll mouse wheel.There's a menu named “XUB” at the top.While in the mode, type 【Ctrl+hm】 (describe-mode) to see inline documentation.Unicode FilesThe mode includes about 20 files of unicode symbols of different categories, used as a character palette. Some of the palette's characters can be seen in the following:Sample Unicode CharactersMath Symbols in Un…