We have now discussed the macros available for defining the basic
parts of a paper and appropriately titling them.
Now let us turn to the most important
stuff – other than text – which appears in each section; namely
equations.
If you've done your homework and read Knuth or First Grade
TEX you know that equations are typed in math mode
and that you let TEX know that you are in math mode by
typing either $ or $$ .
Enclosing an equation inside a pair of single $ signs
puts it in ordinary mode; enclosing the same equation between
matching pairs of $$ signs puts it in display mode.
Regular math mode is used for inserting equations into a line of
text.
Since you have done your homework we don't have to say
anything about this, since PHYZZX doesn't play with ordinary math mode
at all.
Display mode is used for generating equations which are to stand out
from the ordinary text.
It allows you to type
$$ (x+y)(x-y) = xˆ 2 - yˆ 2 $$
in order to get
Displayed equations are used in all journals and are usually
numbered.
In PLAIN TEX there is a built in
capability for allowing you to generate
equation numbers; it is the macro
eqno.
If you type
$$ (x+y)(x-y) = xˆ 2 - yˆ 2
eqno(13) $$
you get
So, you ask, what does PHYZZX have to do with this? Well the answer to that question depends upon who you are. If you are typing someone else's handwritten manuscript which is in final proofread form, then these macros for putting in equation numbers are all you need. If, however, you are the author of the paper, typing it in yourself, either from a rough copy or composing it directly at the terminal, then these two commands leave a great deal to be desired.
To begin with, if you are anything like me, when composing
at the typewriter you usually forget the number of the last
equation you have typed.
Of course you can always go back and look it up, but this is time
consuming and sometimes difficult to do.
In addition if, as is usually the case, you expect the manuscript
to be changed after it is typed, then it is highly likely
that equations will be added, deleted and moved around.
In that case, if you have used
eqno or
leqno
you will have to go through the text and change all of the
equation numbers and all references to those numbers each time
there is a revision.
Clearly this can get to be a big nuisance.
Wouldn't it be nice if TEX would just take care of numbering
all of the equations properly each time it prints the manuscript
taking into account all of the revisions automatically.