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**To**:*math-font-discuss@cogs.susx.ac.uk***Subject**:**Re: (Partial) implementation of new math encodings****From**:*"Nelson H. F. Beebe" <beebe@math.utah.edu>***Date**: Wed, 23 Apr 1997 11:18:03 -0600 (MDT)**Cc**:*beebe@csc-sun.math.utah.edu*

Matthias Clasen <mclasen@sun2.mathematik.uni-freiburg.de> writes: >> I was really thinking of a comparison of the graphical output: perhaps >> more along the lines of using pstopnm on a ps file and then comparing >> the resulting pbm files with pnmarith -difference. I don't know if that >> will produce any useful information (as I haven't tried it yet). Several months ago, I set up a test suite for ghostscript (for which I'm an alpha tester) to do this sort of thing: produce a bitmap representation of the output for a substantial collection of PostScript files, and then check for differences. It turned out to be infeasible: even a change in optimization level on the same machine could produce substantial differences in the output that made the diffs useless. A visual comparision of the screen images from the two versions would not uncover any differences. I discussed this with L. Peter Deutsch, the ghostscript developer, but we did not find a suitable solution. There is one commercial test suite for PostScript, but its cost is too high for the ghostscript developers. Thus, I'm sceptical that diff'ing bitmaps would produce output that a human could reasonably interpret. Even though TeX works internally almost exclusively in 32-bit integer arithmetic, PostScript renderers have a LOT of floating-point, and this may lead to more differences than would be expected. I therefore think a comparison of the output of dvitype or dv2dt would be a better way, since that would avoid the introduction of machine-sensitive floating-point arithmetic. This approach also has the advantage of not requiring software that is not part of standard TeX distributions. ======================================================================== Nelson H. F. Beebe Tel: +1 801 581 5254 Center for Scientific Computing FAX: +1 801 581 4148 Department of Mathematics, 105 JWB Internet: beebe@math.utah.edu University of Utah URL: http://www.math.utah.edu/~beebe Salt Lake City, UT 84112, USA ========================================================================

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