# Re: Equation Array

Julio,

Julio Rojas wrote:

Thanks Paul, I've tried it but the first column is right aligned and
the third is left aligned.



In the alignat* example? Shouldn't be -- the alignment alternates right-left-right, so the first and third columns should have the same alignment. Note that the first column is intentionally left empty, so that the 'maximize' and 'subject to' are in the second column (and hence left-aligned).


I'm kind of new on the subject and the
references I have from a friend make them left and right aligned,
respectively. Is there an standard way of aligning them?



I'm not sure there's a generally accepted standard. I like to put the keywords (maximize, s.t.) in one column, the objective function and LHS of constraints in a second column, the constraint direction (=,<,>) in a third column, the RHS in the fourth column and any indexing stuff in a fifth column, so I usually use eqnarray (critics be damned). If I'm going to use alignat, then I'll put max/s.t. in column 2 (left aligned), the LHS _and_ =/>/< in the third column (right aligned), the RHS in the fourth column (left aligned) and indexing in the fifth column (right aligned), which should work pretty well (it avoids gratuitous space in the middle of the constraints).


I guess it's a matter of taste (unless the constraints get long enough that eqnarray sends the equation numbers into another galaxy).

/Paul


-------------------------------------------------
Julio Rojas
jcredbe...@gmail.com

On Wed, Sep 2, 2009 at 5:11 PM, Paul A. Rubin<ru...@msu.edu> wrote:

Julio Rojas wrote:

Thanks, I've already done that, but no option seems to be of help. I'm
trying to put an integer programing model and every restriction should
be numbered and aligned like:

Maximize Z                                          (1)
Subject to:
Z=sum(Xi)                                             (2)
Xi+Xj<=1                       for all i,j in P, i<j (3)
Xi,Xj in {0,1}                        for all i,j in P (4)

So, some rows are numbered, the left column is left aligned and the
right column is right aligned. How can this numbered array be done?
-------------------------------------------------
Julio Rojas
jcredbe...@gmail.com

2009/9/2 Ignacio García <ignacio.gmora...@gmail.com>:

Julio Rojas <jcredbe...@...> writes:


Dear all, is there a way to individually label some equations of an
equation array? Or some rows from an array?
-------------------------------------------------
Julio Rojas
jcredbe...@...


Please have a look at Help>Math (or Ecuaciones) where you can
find a very fine description of this issue in the section 19,
19.3 and/or 19.4.


Julio,

Actually, I think what you want is in section 19.1.  Inside an equation
array environment, Alt-m n toggles numbering of the entire array (separate
number on each line), while Alt-m Shift-n toggles numbering of just the line
the cursor occupies.

BTW, I too write integer programs.  A while back I came across a reference
to an article ("Avoid eqnarray!" by Lars Madsen, The PracTeX Journal #4,
2006) that claims that eqnarray is somehow evil.  The complaints are mainly
about spacing (including the possibility that equation numbers are
overwritten or crowded off the line).  He recommends AMS math environments
or the mathenv package.  Then again, I came across a post on sci.op-research
that as I recall advocated eqnarray.

Anyway, here's an alternative I found somewhere:

\begin{alignat*}{7}
& \text{maximize } & z= &  & 2x_{1} &  & + &  & 3x_{2} &  & + &  & 4x_{3}\\
& \text{subject to: } &  &  & 44x_{1} &  &  &  &  &  & + &  & 50x_{3} &
\ge900\\
&  &  &  &  &  &  &  &  &  &  &  & \llap{\ensuremath{x_{1},x_{2},x_{3}}} &
\ge0
\end{alignat*}

FWIW,
Paul