How to break long equations with LyX

[Paul A. Rubin]

On 6/20/20 8:00 AM, list_email at icloud.com wrote:
>> On Jun 19, 2020, at 5:14 PM, Paul A. Rubin <parubin73 at gmail.com> wrote:
>>
>> 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
>>
>> <breakeq.lyx>—
> Paul,
>
> I’ve attached an example showing a few things, mainly that Command-(Control-)-Enter works with your equation and the equation from Section 18 of the Math manual but not with my equation.
>
> Jerry
>
>
Jerry,

As explained in my reply to your prior message, the breaking in the 
wrong place issue is apparently caused by the use of balanced [] around 
the chubby part of the formula.

Regarding the rest, I also get a bunch of (apparently harmless) LaTeX 
errors/warnings when I compile it. As to why the version you liked 
failed to be transferable to its intended destination, I have no idea 
about that. Although I have the breqn package installed, I have never 
used it, so I don't know with what other packages (or standard LaTeX 
things) it might be incompatible. The change I made in the previous file 
also works here, and (since it is vanilla LaTeX and does not use the 
dmath environment) should be portable.

Paul

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