[Tex/LaTex] Multiline equation, label once and support page break


I want a multiline equation that labeled once and support page break. If I choose


then the split makes it unable to support page break. I understand that I can use align together with nonumber but I want a smarter way that I don't have to worry. It doesn't matter where the label appears.

A simplified question would be: is there any way that automatically set label on the first line and at the same time the whole equation allows page break?

Best Answer

If I understand you correctly, this is what you are looking for: Some aligned equations that are numbered once in the very beginning (first line) and allow page-breaks? The following code does that.

It uses the align* environment to suppress automatic equation numbering. I wrote the short macro \numberthis which does number the current line of an align* environment and updates the equation counter. Then I patched the align* environment to use it and number the first line. As others mentioned, you also need \allowdisplaybreaks.



\expandafter\appto\csname align*\endcsname{\numberthis}




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