\definemathsimplealign[pdeproblem][

left=3D{\startmathfenced[cases]},

right=3D\stopmathfenced,

align=3D{1:right,2:left,3:left},

strut=3Dyes,

]

\define[1]\eqref{(\in[eq:#1])}

\starttext

A function $u$ is said to be = harmonic in $\Omega$ if

\placeformula[eq:Harmonic]

\startformula

\Delta u =3D 0 = \quad\text{in }\, \Omega.

\stopformula

For a given potential $V$ defined on $\partial\Omega$ and a = smooth function $\phi$ defined on $\partial\Omega$, study here the = PDE

\placeformula

\startformula

\startpdeproblem

\NC - \Delta u \NC =3D 0 \NC \qquad\text{in } \Omega = \NR[eq:Harmonic-1]

\NC \frac{\partial u}{\partial = {\bi n}} \NC =3D V u + \phi \NC

\qquad\text{on } = \partial\Omega \NR[eq:Robin]

\stoppdeproblem

\stopformula

In the above PDE = problem, the boundary condition \eqref{eq:Robin} may be replaced by a = nonlinear condition such as

\startformula

\frac{\partial u}{\partial {\bi n}} \NC =3D V u + u^3 = \qquad\text{on } \partial\Omega,

\stopformula

while the notion of a = harmonic function \eqref{Harmonic} may be replaced with

\startformula

-{\rm div}(a(x)\nabla u) =3D= 0 \quad\text{in }\, \Omega.

\stopformula

\stoptext

% end example = alignedcases.tex

Best = regards: Otared

On 10 Oct 2024, at 07:32, Mikael Sundqvist = <mickep@gmail.com> wrote:

Hi,
A. Bowen: The cases are meant for when you = divide something into
cases, as in the example below with = the absolute value. It is a kind
of inline part of a = formula, and I would claim that when you number an
equation,= you do not number one case of a cases, but the equation. If
you refer to it, you talk abou "the second line in (1)" if = you need to
specify. I also get a bit curious, are you = editor of some math journal
that is typeset by ConTeXt?

A. Braslau: I agree that it is common to put = the brace on the left,
but I insist that it makes more = sense to put it on the right _if_ you
have equation = numbers on the right. If equation numbers are to the
left, = it makes sense to put the brace on the left. Nevertheless, to
put the brace on the left side and numbering on the right is = possible
(see example below). But the equation number in = this case is sitting
in between the two equations, and = that is disturbing. If there would
be three lines, one = could argue that it would sit on the middle one.
Or not = distinguish it from the case where it sits on the middle line.

The good thing is of course that one can do as = one please.

\starttext
\startformula
\abs{x} =3D
= \startcases
   \NC x, \NC x = > 0; \NR
   \NC 0, \NC x =3D 0; = \NR
   \NC -x, \NC x < 0. \NR
\stopcases
\numberhere[eq:foo]
\stopformula

\startformula
\startalign
=    [location=3Dpacked,fences=3Dcases]
=    \NC \[21-(9 - n^2)\NC =3D=E2=96=A1^\prime\]\NR
   \NC n^2+12 \NC=3D=E2=96=A1^\prime. =        \NR
= \stopalign
\numberhere[eq:foo]
\stopformula

\stoptext

/Mikael

On Thu, = Oct 10, 2024 at 2:21=E2=80=AFAM Alan Braslau via ntg-context
<ntg-context@ntg.nl> wrote:

It is common, when writing a = system of equations, to put a brace on the
left. It could = make sense to number this system of equations with a
single = number, on the right and aligned with the right margin. It would
also make sense for this number to be aligned with the middle = of the
two equations of the system.

A brace on the right would not introduce the grouping as a = system of
equations, rather as a pair of equations sharing = a common number.

Alan

On Wed, 9 Oct 2024 12:20:00 = -0400
Alan Bowen <bowenalan03@gmail.com> wrote:

I understand. The = reasoning makes sense to me and, as editor of a
paper in = which this appears, I will ask the author to consider
dropping the brace.

I wonder of = there is some similar thinking underlying the fact that
\startcases... puts the equation number so close to the = equation
itself and not at a margin (typically right).

Again, many thanks, Mikael.
Alan

On Wed, Oct 9, 2024 at = 12:12=E2=80=AFPM Mikael Sundqvist <mickep@gmail.com>
wrote:
Hi,

I think what you ask for was never supported in ConTeXt, for = a
reason. The idea is that either one groups a set of = equations with
a brace and numbers them with one number, = or one does not group,
and then one can number each line = separately/independently.
Grouping on the left with a = brace and numbering one line to the
right is, even if we = see that often, not really logical.

If = there is a large request for doing this, I can talk to Hans about
it, maybe it is easy on the code side to support it. But I = remember
from when we were messing with numbering, and in = particular when
there are alignments, that it is a bit = complicated.

/Mikael

On Wed, Oct 9, 2024 at 5:19=E2=80=AFPM Alan Bowen <bowenalan03@gmail.com>
wrote:

Thank = you, Mikael. That is very helpful and much appreciated.

What I now have is:
\startplaceformula
\startformula
=    \startalign
=      \NC \[21-(9 - n^2)\NC =3D=E2=96=A1^\prime\] = \NR[eq:1]
     \NC = n^2+12 \NC=3D=E2=96=A1^\prime. =          \NR[eq:2]
   \stopalign
= \stopformula
\stopplaceformula
which = put the numbers at the right margin,as I wanted.

So how do I get a brace on the left rather than on the right? = Or
is
there documentation = that explains this?
Alan

On Wed, Oct 9, 2024 at = 10:22=E2=80=AFAM Mikael Sundqvist
<mickep@gmail.com>
wrote:

Hi,

On Mon, Oct 7, 2024 at 11:45=E2=80=AFPM Alan = Bowen
<bowenalan03@gmail.com>
wrote:

I have the following which = works, except for the fact that the
equation number does = not go to the right margin.

\startplaceformula
\startformula[align=3Dmiddle, prefix=3Dno]
\startcases[distance=3D2pt]
\NC \[21-(9 - = n^2)\NC =3D=E2=96=A1^\prime\]\NR
\NC\hfill n^2+12 = \NC=3D=E2=96=A1^\prime.\NR[eq04]
\stopcases
\stopformula
\stopplaceformula

I expect that I have missed something pretty basic here, so = any
guidance will = be greatly appreciated.

Maybe I = misunderstand you, but I do not think cases is right
here. = Also, are you sure you want to group two equations but
only = number one of them.

If I understand you = correctly, I'd try with one of these,
depending on if = citing the group or one of the equations.

\starttext

\startformula
\startalign[location=3Dpacked,fences=3Dsesac]
   \NC \[21-(9 - n^2)\NC =3D=E2=96=A1^\prime\]\= NR
   \NC n^2+12 \NC=3D=E2=96=A1^\prim= e.        \NR
= \stopalign
\numberhere[eq:foo]
\stopformula

\startplaceformula \startformula
=    \startalign
=      \NC \[21-(9 - n^2)\NC =3D=E2=96=A1^\prime\] = \NR%[eq:bar-a]
     \NC = n^2+12 \NC=3D=E2=96=A1^\prime. =          \NR[eq:bar-b]
   \stopalign
= \stopformula
\stopplaceformula

\stoptext

/Mikael

___________= ________________________________________________________________________If your question is of interest to others as well, please = add an entry to the Wiki!

maillist : ntg-context@ntg.nl / = https://mailman.ntg.nl/mailman3/lists/ntg-context.ntg.nlwebpage : https://www.pragma-ade.nl / https://context.aanhet.net (mirror)
archive = : https://github.com/contextgarden/context
wiki=     : https://wiki.contextgarden.net
_______________________________________________________________= ____________________
__________________________________________________= _________________________________
If your question is of = interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / https://mailman.ntg.nl/mailman3/lists/ntg-context.ntg.nlwebpage : https://www.pragma-ade.nl / https://context.aanhet.net (mirror)
archive = : https://github.com/contextgarden/context
wiki=     : https://wiki.contextgarden.net
_______________________________________________________________= ____________________

Otared Kavian

e-mail: = otared@gmail.com

Phone: +33 6 88 26 70 95