I don't understand the difference between the split
and aligned
environments introduced by amsmath, so I'm posting this question as a place to collect what subtle details there may be. One thing observable straight off is that split
only works with two columns, whereas aligned
works with an arbitrary number of columns. But they are similar in other immediately visible ways:
- Both have to be wrapped in another math-introducing environment, like
\begin{equation}...\end{equation}
- Both permit only a single
\tag{...}
for the entire group, not one tag for each line (EDIT: not sure where I got that impression, in fact neither permits any\tag
, thoughaligned
's friendgathered
does permit a single\tag
, as described here)
I searched existing questions on this site about what differences there may be between these environments. I did find this question: Difference between (split, align) and (gather, aligned)?, where---despite the title and phrasing of the question---most of the answers focus just on the difference between the split
and aligned
environments themselves.
EDIT: Collecting the differences noted so far.
As one answer to the above question points out, inside
equation
environments (but not insidegather
oralign
environments), thesplit
andaligned
environments have different vertical spacing from the surrounding text.As another answer to that question points out, when the body of these environments gets very long, their horizontal placement starts to diverge.
As Mico noted in comments, section 3.7 of the
amsmath
User Guide notes thataligned
(together withalignedat
andgathered
) accepts an optional[t]
or[b]
argument, for explicit vertical placement of any equation tags.split
does not accept any such argument.As egreg notes in his answer,
split
will on the other hand honor thetbtags
or (default)centertags
option to theamsmath
package. Whereasaligned
and its friends will not.As Mico's comments also suggested, but I did not immediately appreciate,
split
is not supposed to go together with any other typeset material on the same display line. On the other hand,aligned
and its friends can be freely combined with other unaligned materials, or even other blocks ofaligned
and so on. They will be horizontally juxtaposed and vertically centered. I've explained this further in an answer below.
Perhaps that exhausts the differences between split
and aligned
: though if others know of other differences, please point them out.
amsmath
package? It mentions two important differences -- in addition to the ones you mention in your write-up -- between thesplit
environment on the one hand and thealigned
environment (and its close relatives, thegathered
andalignedat
environments) on the other.split
. Of the two features cited there, the first (permitting additional unaligned text on the same row) doesn't distinguishaligned
and friends (gathered
,alignedat
) fromsplit
, at least that's what my testing shows. The other feature cited there is different between them:aligned
and friends take an optional[t]
or[b]
argument, butsplit
does not.split
is generally used inside environments such asequation
andequation*
, what's said in the first two sentences of the first paragraph of section 3.7 of the user guide (i) does apply tosplit
(even thoughsplit
isn't mentioned "explicitly"...) and (ii) helps set up distinguish what's different aboutaligned
(andgathered
andalignedat
).aligned
also has to be used insideequation
or the like; there is no difference there with respect tosplit
. And if you try it, you'll see that you can add further unaligned text on the sameequation
line, after either of them. That is:begin{equation}\begin{XXX}...\end{XXX}\text{ hello}\end{equation}
gives the same results whetherXXX
isaligned
orsplit
. (And in neither case can thebegin{equation}
or something similar be omitted.)\text
); In that case I tend to usealigned
. I only usesplit
insideequation
s, when I want to split them; but not only a part (because that would be “aligning”), I use split when the whole equation must be divided, hence the construction is always (in my case)\begin{equation}\begin{split} … \end{split}\end{equation}
(orequation*
).