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Since July 2011, there has been a beta release of LM Math. Some people seem to be quite excited about this. The release announcement states that this release

...completes the modernization of the Computer Modern family of typefaces .... the modernization was incomplete without the math fonts of the Comupter Modern family

I understand many reasons to use the lmodern text fonts:

As far as I can tell, none of these advantages apply to the LM Math fonts. So my question is, why did the GUST team feel the need to produce new math fonts? As far as I can tell the only advantage that they quote on their release announcement is that they are "modern", but I fail to find "new" a compelling argument. Why would I use a newer, less-tested font (that, if it is anything like the other LM fonts, is likely less well-hinted than bluesky/ams/y&y CM)?

I understand that this in an early beta release, so it is not suprising that there is not much (any?) documentation or rationale accompanying the fonts, but I hope someone here knows the reason for them.

EDIT: I looked a bit harder, and I saw that my installation of the lm package, version 2.004, 30.10.2009 already includes math fonts. In LaTeX I can use them by default \usepackage{lmodern}, or not by \usepackage[nomath]{lmodern}. The README says that these 20 math fonts are "at the moment a duplicate of PL math fonts", which presumably refers to these fonts. So, presumably, this new LM Math release is to replace these PL math fonts with something else. So, in addition to my question about what was wrong with the bluesky/ams/y&y CM math I'd also be interested to know: what was wrong with the PL math fonts?

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Well, you can use LM Math in Microsoft Office or other softwares. That's an advantage for many people. –  Leo Liu Aug 11 '11 at 10:16
    
@Leo, true, but the excited posting from Marcin Borkowski I linked at the beginning describes that as a "downside", so I'm presuming there is also some good advantages for TeX users. –  Lev Bishop Aug 11 '11 at 21:16
    
Hah, just found this post. Well, it was kind of a joke from my side, please don't take it too seriously! –  mbork Mar 7 '12 at 15:15
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2 Answers

The LM Math fonts are available in OTF Math format. As such they are usable with unicode-math and ConTeXt Mk IV. So you can finally use LM when using Xe/LuaTeX + unicode-math or ConTeXt (as LM + STIX Math just looks horrible). Presumably they also added additional symbols as Unicode defines lots of math symbols that aren't available in the CM math fonts.

As I read the announcement, you can't use the fonts without an OTF capable TeX engine. So with pdflatex, you have to continue to use the old fonts anyway (see the comments for a qualification of this statement).

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Actually, pdftex can use OTF (although it will not subset the glyphs). For example, the LM-Math can be accessed in plain tex with \pdfmapline{+test LMMath-Regular <<LMMATH-v0903.otf}\font\tst=test\tst testing\bye. (I constructed test.tfm with LCDF typetools and the commandline otftotfm -n test --no-encoding --no-map LMMATH-v0903.otf). Presumably that's not enough to use the mathematical features of the font, but it does show that you can use otf with pdftex. –  Lev Bishop Aug 10 '11 at 20:08
    
The Xe/LuaTeX + unicode-math part, I think I understand. The ConTeXt part, I do not. As far as I can tell ConTeXt always supported LM and math: for example \starttext $x^2$\stoptext produces a PDF that uses the font LMMathItalic12-Regular (I used context live to check this). –  Lev Bishop Aug 10 '11 at 20:55
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@Lev: though pdflatex can use OTF fonts in very basic way, it doesn't make use of any layout tables including MATH table in LM Math, and I don't think it can access more than 256 glyphs from the font. Regarding ConTeXt, context live is "MK II" which is pdflatex based, however "MK IV" can indeed use LM type1 math fonts, but it is kind of a hack until the proper OTF font is available (and the texlive 2011 version is now using it). –  Khaled Hosny Aug 10 '11 at 21:49
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@Lev: I have to admit that I don't know much about TeX's fonts handling. For me the reason I'm happy to see the LM Math OTF fonts is that it gives me more choice when using unicode-math (and I use that quite a lot). Also having the TeX math font available might increase the interest in Unicode-enabled math typesetting, which in turn will hopefully cause the maintainers of related packages and engines to fix bugs faster. –  Caramdir Aug 11 '11 at 0:03
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Let me provide a different take on this. This has more to do with the fact why unicode enabled math typesetting is useful, but does illustrate why opentype math fonts help.

ConTeXt allows you to export a TeX document to XML. In such an export math is exported to MathML.

Using an opentype math font allows you to look at the final glyph that is inserted into the pdf, and use that in the exported MathML. For example, $\Gamma$, which is normally typeset upright, is exported to <math><mi>0x0393</mi></math>. However, if you set an appropriate option so that uppercase Greek letters are typeset in italic, then $\Gamma$ is exported to <math><mi>0x1D6E4</mi></math>. The export functions do not care how the mapping from $\Gamma$ to the appropriate font glyph is done. It simply uses the opentype slot of the final glyph in the exported MathML.

Of course, it is still possible to implement such an export with Type1 fonts. However, in that case, the export functions will need to understand the mappings from macros (or input characters) to unicode slots. Thus, the macro package needs to implement two mappings: (i) input character to font glyph; (ii) input character to opentype location. With an opentype math font, these two mappings collapse to one. For this reason, even type1 math fonts are converted into a fake opentype math font on the fly in ConTeXt MkIV.

It is also possible (although not currently implemented) to embed the converted MathML into the pdf file so that a screen reader will read the mathematical expression correctly. This will improve the accessibility of TeX documents. Another advantage is that if you copy a math expression from a pdf and pastes it in a text file, the resulting MathML will be pasted. Wrap it around an appropriate environment, and then you can compile the expression with TeX again and recover the original math expression. (ConTeXt has a module for typesetting MathML; I haven't checked whether the LaTeX XML packages allow typesetting of MathML). This is similar to using an appropriate cmap file so that you can copy and paste text.

Using an opentype math fonts makes it easier to implement such features. And, of course, if you want a good looking pdf, you need a good (and preferably free) math fonts. Currently they are in short supply; so a new opentype math font is a welcome addition.

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