Hcfyk

Is there any way to reduce the distance inside σ₀ and between sigma and its subscript in general in the following setup automatically? That is, each time you type in sigma_0 (or sigma_1 etc.), you wish the actual output to be more consistent with sigma_{!0} (or sigma_{!1} etc.).

Input:

documentclass{book}

usepackage{fontspec}

usepackage[american,british,french,norsk,german,ngerman]{babel}

usepackage{mathtools}

mathtoolsset{mathic=true} %%% See http://tex.stackexchange.com/a/3496/

usepackage{amssymb}

usepackage{unicode-math}

setmainfont[Ligatures=TeX]{TeX Gyre Termes}

setsansfont{TeX Gyre Heros}[Scale=0.88]

setmonofont{TeX Gyre Cursor}

setmathfont[Ligatures=TeX]{TeX Gyre Termes Math}

setmathfont[Ligatures=TeX,range={setminus}]{Asana Math}

setmathfont[Ligatures=TeX,Extension=.otf,range={"2A3E},BoldFont=XITSMath-Bold]{XITSMath-Regular}%%% The fat semicolon

usepackage[babel=true,verbose=errors]{microtype}

begin{document}

[sigma_0 sigma_0]

[sigma_{!0} sigma_{!0}]

end{document}

Output so far:

As you see, in the upper line the left zero seems to be more close to the right σ (which doesn't make any sense) than to the left one (which would make sense). The kerning in the lower line makes more sense.

I guess, this would be easier than Subscript kerning for specific letters in XeLaTeX, since we already have sigma as a macro and can redefine it.

For which letters in the subscript position the kerning should be improved (and how) is intentionally left unspecified; improving the kerning in sigma_<any single arabic digit or any single Latin small letter> would suffice as a start. Of course, for σ_{mathrm{T}} we might need less kerning (e.g., only -1mu rather than -3mu), and that's why capital Latin letters would need more work (and are not asked for in the first step). As of now, I intend to use the following subscripts: all the digits, i, j, k, k (yes, this one upright), n, i + 1, i - 1.

The following definition does it:

ExplSyntaxOn

cs_new_eq:NN __userxlixk_actual_sigma: sigma

RenewDocumentCommandsigma{}

  { __userxlixk_sigma: }

cs_new_protected:Npn __userxlixk_sigma:

  {

    peek_catcode_remove:NTF c_math_subscript_token

      { __userxlixk_sigma_check_group:n }

      { __userxlixk_actual_sigma: }

  }

cs_new_protected:Npn __userxlixk_sigma_check_group:n #1

  {

    tl_if_single_token:nTF {#1}

      { __userxlixk_actual_sigma: c_math_subscript_token { ! #1 } }

      { __userxlixk_actual_sigma: c_math_subscript_token {#1} }

  }

ExplSyntaxOff

I save the definition of sigma in __userxlixk_actual_sigma: then redefine sigma to check:

1. if it is followed by a c_math_subscript_token: if it is not, then just print __userxlixk_actual_sigma: otherwise;




2. grab what follows the subscript token as argument and check if the argument consists of a single token: if it does, apply a !, otherwise print normally.

Here's the output before and after the redefinition (I used LuaTeX and lua-visual-debug to show the negative kern):

Code:

documentclass[varwidth]{standalone}

usepackage{lua-visual-debug}

usepackage{luatexbase}

usepackage{unravel}

usepackage{fontspec}

usepackage[american,british,french,norsk,german,ngerman]{babel}

usepackage{mathtools}

mathtoolsset{mathic=true} %%% See http://tex.stackexchange.com/a/3496/

usepackage{amssymb}

usepackage{unicode-math}

setmainfont[Ligatures=TeX]{TeX Gyre Termes}

setsansfont{TeX Gyre Heros}[Scale=0.88]

setmonofont{TeX Gyre Cursor}

setmathfont[Ligatures=TeX]{TeX Gyre Termes Math}

setmathfont[Ligatures=TeX,range={setminus}]{Asana Math}

setmathfont[Ligatures=TeX,Extension=.otf,range={"2A3E},BoldFont=XITSMath-Bold]{XITSMath-Regular}%%% The fat semicolon

usepackage[babel=true,verbose=errors]{microtype}

begin{document}

$sigma_{abc} sigma_0 sigma_0$



ExplSyntaxOn

cs_new_eq:NN __userxlixk_actual_sigma: sigma

RenewDocumentCommandsigma{}

  { __userxlixk_sigma: }

cs_new_protected:Npn __userxlixk_sigma:

  {

    peek_catcode_remove:NTF c_math_subscript_token

      { __userxlixk_sigma_check_group:n }

      { __userxlixk_actual_sigma: }

  }

cs_new_protected:Npn __userxlixk_sigma_check_group:n #1

  {

    tl_if_single_token:nTF {#1}

      { __userxlixk_actual_sigma: c_math_subscript_token { ! #1 } }

      { __userxlixk_actual_sigma: c_math_subscript_token {#1} }

  }

ExplSyntaxOff



$sigma_{abc} sigma_0 sigma_0$

end{document}

Note, however, that this code will work if you use sigma_a^b but not if you use sigma^b_a.

I'd use the e argument type of xparse.

documentclass{book}

usepackage{fontspec}

usepackage[american,british,french,norsk,german,ngerman]{babel}

usepackage{mathtools}

usepackage{amssymb}

usepackage{unicode-math}

usepackage[babel=true,verbose=errors]{microtype}



setmainfont{TeX Gyre Termes}

setsansfont{TeX Gyre Heros}[Scale=0.88]

setmonofont{TeX Gyre Cursor}

setmathfont{TeX Gyre Termes Math}

setmathfont{Asana Math}[

  range={setminus},

]

setmathfont{XITSMath-Regular}[

  Extension=.otf,

  range={"2A3E},

  BoldFont=XITSMath-Bold,

]



%mathtoolsset{mathic=true} %%% See http://tex.stackexchange.com/a/3496/



AtBeginDocument{%

  letstandardsigmasigma

  letsigmakernedsigma

}



NewDocumentCommand{kernedsigma}{e{_^}}{%

  standardsigma

  IfValueT{#1}{_{!#1}}%

  IfValueT{#2}{^{#2}}%

}



begin{document}



[sigma_0 sigma_0^2 sigma^2_0]

[standardsigma_{!0} standardsigma_{!0}^2 standardsigma^2_{!0}]



end{document}