How to break long equations with LyX

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> 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