How to break long equations with LyX

[Paul A. Rubin]

On 6/19/20 7:34 PM, list_email at icloud.com wrote:
>> On Jun 19, 2020, at 8:15 AM, Paul A. Rubin <parubin73 at gmail.com> wrote:
>>
>> On 6/19/20 7:51 AM, list_email at icloud.com wrote:
>>> I have tried mightily to get LyX to break long equations. I’ve studied multiple pages at stackexchange, both LaTeX and LyX, and can’t seem to get anything to work.
>>>
>>> I have had luck in the past with the second large block of code at this page:
>>>
>>> https://stackoverflow.com/questions/2904807/lyx-breaking-long-formula-lines
>>>
>>> but today I have some problems with it.
>>>
>>> First, it doesn’t work if the \text command appears inside my own LaTeX code that appears between \begin{dmath} and \end{dmath} or if I try to use the trick twice in the same document. (That’s a tentative analysis of the problem.) Specifically, LyX runs at 100% CPU eventually gives me a chance to abort and then follows up with this additional message: "The external program pdflatex finished with an error. It is recommended you fix the cause of the external program's error (check the logs)."
>>>
>>> Plus, I now want to to apply the line breaking to a line within an aligned environment (Insert -> Math -> Aligned Environment in the menu system.) This is causing things to look even worse, even though I added two “aligned” lines to the referenced code block. (If you look at the code you’ll see the obvious places to add the lines.)
>>>
>>> How do LyX-ers handle this? Is there “LyX” solution to breaking long equations? I’m OK with some ad hoc solution for now, or some ERT if it works.
>>>
>>> Thanks,
>>> Jerry
>>>
>>>
>> I've never used the breqn package, but with ordinary and AMS math environments, hitting Ctrl-Enter in the middle of a long formula will break it (inserting a line break, \\, in the LaTeX output). If that doesn't achieve what you want, perhaps you could post a minimal example and a specification of what the output should look like.
>>
>> Paul
>>
> Thanks, Paul. I’m on a Mac so of course Control-Enter has no meaning. Usually this translates to Mac-speak as Command-Enter. When I do Command-Enter in my equation, which is unfortunately inside a align environment, it instead adds a row to the matrix that represents the align environment. Ditto for Shift-Command-Enter. These two commands in LyX are mapped as Insert -> Formatting -> Ragged Line Break and Justified Line Break, respectively but invoking the menu commands with the cursor in my equation has exactly the same effect: adding a row to the align matrix (above the row where the cursor is.) When (Shift-)Command-Enter is done to a non-align display equation a similar thing happens except now the non-align equation is converted to an align equation with a blank new row _below_ the original equation.
>
> Right now I guess I would be pretty happy with merely a way to make Command-shift (Control-shift) do what is expected which is apparently break the equation instead of creating a new row.
>
> Jerry
>
Jerry,

I just created an align environment with two equations, the left side of 
the first being ridiculously long. When I put the cursor somewhere 
toward the middle of the left side of the long equation and inserted a 
break (using Ctrl-Enter -- I'll get to the Mac part in a minute), it 
broke the equation and inserted a new row. So

     (x+x+x+x+...+x) =1
      y =2

(where the right column contained the equal signs and integers) became

     (x+x+x+...
     +x+x+x+x) =1
      y =2

where the right column is empty in the first row. See the attached 
minimal example. Is this not what you want?

Regarding the key mapping, if you can find an unused key combo that you 
have a chance of remembering, you can map it to "newline-insert newline" 
using Tools > Preferences... > Editing > Shortcuts. That's what 
Ctrl+Enter binds to for me.

Paul

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