Add subequations module and example (#10029)

The module allows to use the subequations environment.

There is still a pending request to implement this environment
natively in LyX's mathed.

Contributed by Joel Kulesza.

lib/Makefile.am

@@ -363,6 +363,7 @@ dist_examples_DATA = \
 	examples/splash.lyx \
 	examples/spreadsheet.lyx \
 	examples/sweave.lyx \
+	examples/subequations.lyx \
 	examples/tufte-book.lyx \
 	examples/tufte-handout.lyx \
 	examples/varwidth-floats-side-by-side.lyx \
@@ -2265,6 +2266,7 @@ dist_layouts_DATA =\
 	layouts/stdstarsections.inc \
 	layouts/stdstruct.inc \
 	layouts/stdtitle.inc \
+	layouts/subequations.module \
 	layouts/svcommon.inc \
 	layouts/svglobal.layout \
 	layouts/svglobal3.layout \

lib/examples/subequations.lyx

@@ -0,0 +1,254 @@
+#LyX 2.2 created this file. For more info see http://www.lyx.org/
+\lyxformat 508
+\begin_document
+\begin_header
+\save_transient_properties true
+\origin unavailable
+\textclass article
+\use_default_options true
+\begin_modules
+subequations
+\end_modules
+\maintain_unincluded_children false
+\language english
+\language_package default
+\inputencoding auto
+\fontencoding global
+\font_roman "default" "default"
+\font_sans "default" "default"
+\font_typewriter "default" "default"
+\font_math "auto" "auto"
+\font_default_family default
+\use_non_tex_fonts false
+\font_sc false
+\font_osf false
+\font_sf_scale 100 100
+\font_tt_scale 100 100
+\graphics default
+\default_output_format default
+\output_sync 0
+\bibtex_command default
+\index_command default
+\paperfontsize default
+\spacing single
+\use_hyperref false
+\papersize default
+\use_geometry false
+\use_package amsmath 1
+\use_package amssymb 1
+\use_package cancel 1
+\use_package esint 1
+\use_package mathdots 1
+\use_package mathtools 1
+\use_package mhchem 1
+\use_package stackrel 1
+\use_package stmaryrd 1
+\use_package undertilde 1
+\cite_engine basic
+\cite_engine_type default
+\biblio_style plain
+\use_bibtopic false
+\use_indices false
+\paperorientation portrait
+\suppress_date false
+\justification true
+\use_refstyle 1
+\index Index
+\shortcut idx
+\color #008000
+\end_index
+\secnumdepth 3
+\tocdepth 3
+\paragraph_separation indent
+\paragraph_indentation default
+\quotes_language english
+\papercolumns 1
+\papersides 1
+\paperpagestyle default
+\tracking_changes false
+\output_changes false
+\html_math_output 0
+\html_css_as_file 0
+\html_be_strict false
+\end_header
+
+\begin_body
+
+\begin_layout Standard
+The 
+\family typewriter
+subequations
+\family default
+ environment, provided by the 
+\family typewriter
+amsmath
+\family default
+ package, is helpful to group logically-linked equations.
+ For example, the one-speed one-dimensional integro-differential equation
+ with 
+\begin_inset Formula $0\le x\le X$
+\end_inset
+
+ and 
+\begin_inset Formula $-1\le\mu\le1$
+\end_inset
+
+ shown in Eq.
+\begin_inset space ~
+\end_inset
+
+
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "eq:odoglbe"
+
+\end_inset
+
+ has associated boundary conditions shown in Eqs.
+\begin_inset space ~
+\end_inset
+
+
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "eq:rlbc"
+
+\end_inset
+
+ and 
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "eq:vrbc"
+
+\end_inset
+
+.
+\begin_inset Flex Subequations
+status open
+
+\begin_layout Plain Layout
+\begin_inset Formula 
+\begin{align}
+\mu\frac{d\psi\left(x,\mu\right)}{dx}+\Sigma_{t}\left(x\right)\psi\left(x,\mu\right) & =\intop_{-1}^{1}\frac{\Sigma_{s}\left(x,\mu'\to\mu\right)}{2}\psi\left(x,\mu'\right)d\mu'+\frac{Q\left(x,\mu\right)}{2},\label{eq:odoglbe}\\
+\psi\left(0,\mu\right) & =\psi\left(0,-\mu\right)\,,\,0<\mu\le1,\label{eq:rlbc}\\
+\psi\left(X,\mu\right) & =0\,,\,-1\le\mu<0.\label{eq:vrbc}
+\end{align}
+
+\end_inset
+
+
+\begin_inset CommandInset label
+LatexCommand label
+name "eq:odoglbeset_aligned"
+
+\end_inset
+
+
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+In the previous case, the equations use the 
+\family typewriter
+amsmath
+\family default
+ 
+\family typewriter
+align
+\family default
+ environment; however, this is not necessary as shown in Eqs.
+\begin_inset space ~
+\end_inset
+
+
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "eq:odoglbenoa"
+
+\end_inset
+
+–
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "eq:vrbcnoa"
+
+\end_inset
+
+.
+ 
+\begin_inset Flex Subequations
+status open
+
+\begin_layout Plain Layout
+\begin_inset Formula 
+\begin{equation}
+\mu\frac{d\psi\left(x,\mu\right)}{dx}+\Sigma_{t}\left(x\right)\psi\left(x,\mu\right)=\intop_{-1}^{1}\frac{\Sigma_{s}\left(x,\mu'\to\mu\right)}{2}\psi\left(x,\mu'\right)d\mu'+\frac{Q\left(x,\mu\right)}{2},\label{eq:odoglbenoa}
+\end{equation}
+
+\end_inset
+
+
+\begin_inset Formula 
+\begin{equation}
+\psi\left(0,\mu\right)=\psi\left(0,-\mu\right)\,,\,0<\mu\le1,\label{eq:rlbcnoa}
+\end{equation}
+
+\end_inset
+
+
+\begin_inset CommandInset label
+LatexCommand label
+name "eq:odoglbeset_individual"
+
+\end_inset
+
+
+\begin_inset Formula 
+\begin{equation}
+\psi\left(X,\mu\right)=0\,,\,-1\le\mu<0.\label{eq:vrbcnoa}
+\end{equation}
+
+\end_inset
+
+
+\end_layout
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+As an alternative to cross-referencing each subequation directly, the group
+ of subequations (i.e., Eq.
+\begin_inset space ~
+\end_inset
+
+
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "eq:odoglbeset_aligned"
+
+\end_inset
+
+ and/or Eq.
+\begin_inset space ~
+\end_inset
+
+
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "eq:odoglbeset_individual"
+
+\end_inset
+
+) can be referenced by placing a label within the subequation inset but
+ outside the equation(s).
+\end_layout
+
+\end_body
+\end_document

lib/layouts/subequations.module

@@ -0,0 +1,19 @@
+#\DeclareLyXModule{Subequations}
+#DescriptionBegin
+#Provide a straightforward way to segregate subequations in LyX. See the subequations.lyx example file.
+#DescriptionEnd
+
+# Author: Joel A. Kulesza (jkulesza@gmail.com)
+
+Format 48
+
+InsetLayout Flex:Subequations
+  LyxType               custom
+  Decoration            classic
+  LabelString           Subequations
+  LatexType             Environment
+  LatexName             subequations
+  MultiPar              true
+  Requires              amsmath
+End
+