Re: [Groff] digits in eqn

[Dean Allen Provins, P. Geoph.]

Ted:

On Wed, Aug 01, 2007 at 11:00:10PM +0100, Ted Harding wrote:
> Hi Folks,
> 
> I'm trying to overcome an eqn "phenomenon" -- in some ways a
> "feature", in others a "bug".
> 
> What I'm referring to can be seen if you set the following
> in Times, using a fairly large point size (say 15) (I'm using
> ms macros here):
> 
> .nr DD 0
> .EQ I
> 21 ~~=~~ 3 times 7
> .EN
> .EQ I
> 22 ~~=~~ 2 times 11
> .EN
> 
> You wil see that the "=" signs do not line up.
> 
> It seems that eqn uses the glyph-width of the digits in computing
> the layout, as opposed to the normal metrics. In TR, digits have
> fixed width, so, while one would expect the "=" signs in the above
> to line up, they don't -- since the "1" glyph is narrower than the
> "2" glyph, and eqn therefore packs it closer to the "2".
> 
> I reckon this is an instance of "bug" behaviour, since it can spoil
> the layout of a stack of equations.
> 
> It is possible to overcome this by using constructs like
> 
> .EQ I
> 2{roman "1"} ~~=~~ 3 times 7
> .EN
> .EQ I
> 22 ~~=~~ 2 times 11
> .EN
> 
> but that is very clumsy (you have to use the "roman" attribute,
> since otherise the "1" comes out italic).
> 
> I've been looking for a simpler way to turn this off. None of the
> "customisation" variables listed for eqn seems to have anything
> to do with this.
> 
> One can of course also handle it by writing the equations as a
> matrix, like:
> 
> .EQ I
> set column_sep 40
> matrix {
>  lcol { 21 above 22 }
>  lcol { = above = }
>  lcol {{3 times 7} above {2 times 11}}
> }
> .EN
> 
> but (a) this too is very complicated, (b) the spacing between
> "2" and "1" in "21" is still too narrow (just doesn't look right).
> 
> I should add that the above is just a simple example, for illustration.
> In real life, I hit this problem with long equations which have
> several subscripts or superscripts, e.g.:
> 
> .nr DD 0
> .EQ I
> define Exp %{ type "operator" roman "E" ^ }%
> 
> {partial b sub 1} over {partial theta sub 1}
>   Exp ( tau sub 1 ( y ) ) ~+~
> {partial b sub 2} over {partial theta sub 1}
>   Exp ( tau sub 2 ( y ) ) ~+~
> {partial c} over {partial theta sub 1} ~~=~~0
> .EN
> .EQ I
> {partial b sub 1} over {partial theta sub 2}
>   Exp ( tau sub 1 ( y ) ) ~+~
> {partial b sub 2} over {partial theta sub 2}
>   Exp ( tau sub 2 ( y ) ) ~+~
> {partial c} over {partial theta sub 2} ~~=~~0
> .EN
> 
> which gets noticeably out of line as a result of this effect,
> and would be impossibly cumbersome to correct using "local"
> modifications like the above. So I'd just like to turn it off!
> 
> Anyone know something I don't know? Or is one stuck with it?
> 
> With thanks,
> Ted.

I'm a little late getting to this list, and you probably have an
acceptable solution, but here's mine anyway.

Use 'mark' and 'lineup' as per:

.NH
Ted's Lineup Problem
.LP
.nr DD 0
.EQ I
21 ~~=~~ 3 times 7
.EN
.EQ I
22 ~~=~~ 2 times 11
.EN
.NH
Solution - Use 'mark' and 'lineup'
.LP
.nr DD 0
.EQ I
21 ~~ mark =~~ 3 times 7
.EN
.EQ I
22 ~~ lineup =~~ 2 times 11
.EN

The equal signs line up properly this way.

Dean

-- 
                           Dean Provins, P. Geoph.
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