RE: [Groff] Greek Letters

[Ted Harding]

On 25-Mar-03 Sai Sarva wrote:
> 
> Hi, I am pretty new to groff and would really appreciate
> any help.
> 
> When writing eqns using .EQ, the greek letters are
> slanted/italic. When I try specifing 'gfont R' to make them
> erect, it makes no difference, though it would work on a
> sun machine with an old version of troff.
> 
> Any thoughts?
> Many thanks

I assume you're using PostScript output (troff device devps).

Greek letters coming out in italic is ultimately due to the fact
that their troff names are \[*a] (alpha), ... , \[*A] (ALPHA), ...
and these are searched for in the "special" fonts named in the
file DESC in the directory for the device (devps for PostScript),
typically /usr/share/groff/font/devps. DESC for devps lists two
special font desctiption files for symbols: SS and S (in that order).
S refers to the standard Adobe Symbol font, in which Greek letters
are Roman (apologies to Hellenophiles). SS is a modification of S,
whereby PostScript code modifies the shapes of some characters
(notably the Greek letters) by slanting them. The troff name \[*a]
for "alpha" is searched for in the "special" font descriptors, and
since these occur in the order SS S it is first found in SS. Therefore
alpha comes out Italic, normally. This also will be true in ordinary
text (e.g. if you write in Greek) as well as in equations. This is
why your attempt to change it by "gfont R" won't work: "alpha" is
called by "\[*a]" regardless, and "\[*a]" is found in font SS.

However, the troff name \[*A] for upper-case "Alpha" does not occur
on SS (likewise for all upper-case Greek), so it is not found
when SS is searched but is found when S is subsequently searched.

What is going on here is far from simple, since it depends on a lot
of builtin assumptions about how mathematics should be printed,
which are implemented by mechanisms which are located in several
different parts of troff and eqn. In particular, the font description
files S and SS differ in that the troff names for many Greek characters
(such as all upper-case Greek characters) are only in S, while these
characters are "nameless" in SS: therefore their names are not found
when the "Symbol-Slanted" font SS is searched, so they are then
searched for in S (and found) so that they print upright and not
italic. For an example, see the comments below, near the end, about
Upsilon, Gamma  and Sigma.

There is more than one way to make your Greek Roman. A global and
once-and-for-all solution is to simply edit the DESC file so that
the line

  fonts ... SS S ...

reads

  fonts ... S SS ...

However, this is radical, permanently alters the way troff (etc)
works, and being global may achieve effects which you do not want.

At the other extreme, you can do this when needed by using the ".char"
request to force any chosen Greek letters to be set in S font rather
than SS, or vice versa, at any time:

.char \[*a] \f[S]\[*a]\fP
.char \[*b] \f[S]\[*b]\fP
  ...
to get Greek lower-case in Roman, and
.char \[*A] \f[SS]\[*A]\fP
.char \[*B] \f[SS]\[*B]\fP
  ...
to get Greek upper-case in Italic,

and you can revert to the original situation with

.rchar \[*a]
.rchar \[*b]
  ...
.rchar \[*A]
.rchar \[*B]
  ...

which undoes the special definitions, so that troff then searches
for "\[*a]" etc in the usual way and finds them in SS as before,
and finds "\[*A]" in S as before.
You could encapsulate the above in macros like

.de GrRom
.char \[*a] \f[S]\[*a]\fP
.char \[*b] \f[S]\[*b]\fP
  ...
..

.de /GrRom
.rchar \[*a]
.rchar \[*b]
  ...
..

and then whenever you want to switch to Roman Greek lower case
you invoke
.GrRom
and whenever you want to switch it off you invoke
./GrRom

To do the above you will want to know the troff names of all
the Greek characters, so here they are, taken from font S:

*a      alpha
*b      beta
*x      chi
*d      delta
*e      epsilon
*f      phi
*g      gamma
*y      eta
*i      iota
+f      phi1
*k      kappa
*l      lambda
*m      mu
*n      nu
*o      omicron
*p      pi
*h      theta
*r      rho
*s      sigma
*t      tau
*u      upsilon
+p      omega1
*w      omega
*c      xi
*q      psi
*z      zeta

*A      Alpha
*B      Beta
*X      Chi
*D      Delta
*E      Epsilon
*F      Phi
*G      Gamma
*Y      Eta
*I      Iota
+h      theta1
*K      Kappa
*L      Lambda
*M      Mu
*N      Nu
*O      Omicron
*P      Pi
*H      Theta
*R      Rho
*S      Sigma
*T      Tau
*U      Upsilon1
---     Upsilon
ts      sigma1
*W      Omega
*C      Xi
*Q      Psi
*Z      Zeta

(The name in the first column is invoked by the escape sequence
\[name], e.g. the name *a for alpha is invoked as \[*a])

\[*U] in S is the cursive Greek upper-case Upsilon, with PostScript
name Upsilon1; Upsilon ("Y") does not have a troff name (given as
"---" in S, also in SS). You can, however, refer to it by number as
  \f[S]\N'85'\fP
and you will find that it prints like an upper-case Y, or
  \f[SS]\N'85'\fP
if you want it slanted. Therefore you can include
  .char \[*U] \f[S]\N'85'\fP
in your character definitions if you want to use this glyph (like "Y")
rather than what you would otherwise get from \[*U].

You will also find the Greek capital letters do not have names in SS
(i.e. they are given as "---"): this means that their names are not found
when SS is searched, so the search proceeds to S where their names are
found. This ensures conformity with mathematical usage where (for
instance) the gamma function

.EQ
Gamma ( x )
.EN

comes out with a non-italic upper-case Gamma, and likewise for
upper-case Sigma (used for summation). However, this means that
you cannot get slanted upper-case Greek letters at all unless
you define them specially, as above.

Therefore you may need to be careful, in typesetting mathematics,
about which Greek characters you include in your list of Greek
characters defined using .char, since conceivably you may end up
violating some convention of mathematical printing. However, if you
are writing Greek text then you may want to include everything.
This is one advantage of making you changes in macros: you can have
different macros for different purposes.

I hope this helps -- but I admit it's not simple!

All best wishes,
Ted.


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E-Mail: (Ted Harding) <address@hidden>
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Date: 25-Mar-03                                       Time: 10:24:38
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