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COMPUTING SCIENCE

Writing Math on the Web

The Web would make a dandy blackboard if only we could scribble an equation

Brian Hayes

Let the Browser Do It

As we have just seen, translation software can run on the author’s computer or on a server. There is one more possibility: performing the translation on the reader’s computer, or what is known as “the client side.” Under this plan, TeX or some other encoding of mathematical content is written into the Web document and passed along unchanged by the server, to be interpreted by the browser.

Of course the problem with sending TeX to the browser is that the browser has no idea what to do with it. That issue can be addressed by means of a plug-in—a software component installed within the browser.

The best known mathematical plug-in is techexplorer, a program initially developed by Robert S. Sutor at IBM and now maintained and distributed by Integre Technical Publishing. Techexplorer can display complete LaTeX documents or it can render just the mathematical expressions within an HTML document. In either case the display of equations is based on fonts rather than images.

The big advantage of a software plug-in is that the rendering of mathematics is liberated from all the constraints of HTML. The plug-in can supply its own fonts and can place characters with as much precision as the hardware will allow. The big disadvantage is that none of this magic works until the end user downloads and installs the plug-in. This barrier to entry tends to discourage casual visitors to a Web site. It also creates a threshold effect: Authors hesitate to rely on the technology until enough readers adopt it, and vice versa.

An interesting alternative to a plug-in might be called a slip-in. The idea is to bundle up the translator program and include it as part of the Web page itself. There’s no need for the user to install any software; the translation program runs automatically when the page is loaded into a browser. A program of this kind called jsMath takes advantage of the JavaScript programming language built into Web browsers.

JsMath is the creation of Davide P. Cervone of Union College in Schenectady, N.Y. Cervone undertook the project mainly to meet his own needs: He wanted to distribute class notes and homework assignments via the Web, and none of the available solutions were entirely satisfactory. So he wrote what amounts to a TeX interpreter in a JavaScript program.

JsMath offers three styles of equation rendering. The most graceful display requires a set of six fonts based on the Computer Modern faces introduced by Knuth; those fonts are freely available, but jsMath can access them only if the reader downloads and installs them. A fallback strategy is to assemble equations from individual character images. The full set of images—some 78 megabytes worth—is stored on the server; only the subset needed is downloaded with any particular document. The third option is to build equations from Unicode fonts. The reader selects one of the three rendering methods through a pop-up control panel.

Squeezing a TeX interpreter into a Web page is an impressive feat, but it adds considerable bulk and complexity. Documents with many equations take a while to finish rendering. Cervone is now launching a follow-on project called MathJAX, supported by several publishers of mathematical software. The aim is to make the system more flexible and responsive.




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