Jannik, You are right. \nabla looks much nicer and is placed correctly. (I still think the \triangledown placement is slightly off.) My environment files from MkII days have \def\nabla{\triangledown}, so I never tried the true \nabla until your suggestion. Thank you. -Sanjoy Jannik Voges writes:

I think you are using the wrong symbol. Or at least I would prefer \nabla as gradient operator.

Jannik

I cannot say whether the wrong placement is due to the wrong font metrics or the wrong mapping (mathop vs mathord) by ConTeXt.

I tried '\triangle T' (often used as the Laplacian operator, instead of writing it out as \nabla^2). That one comes out fine, even though \triangledown does not. But they seem to have similar kinds of defintions/mappings:

From luatex-math.tex :

\def\triangle {\Umathchar "0"0"0025B3 } \def\triangledown {\Umathchar "2"0"0025BD } So it must be a wrong font metric? -Sanjoy

On Fri, 11 Apr 2014, Aditya Mahajan wrote:

On Fri, 11 Apr 2014, Sanjoy Mahajan wrote:

...

...

I cannot say whether the wrong placement is due to the wrong font metrics or the wrong mapping (mathop vs mathord) by ConTeXt.

I tried '\triangle T' (often used as the Laplacian operator, instead of writing it out as \nabla^2). That one comes out fine, even though \triangledown does not. But they seem to have similar kinds of defintions/mappings:

From luatex-math.tex :

\def\triangle {\Umathchar "0"0"0025B3 } \def\triangledown {\Umathchar "2"0"0025BD }

So it must be a wrong font metric?

AFAIU, ConTeXt does not use luatex-math.tex. The mappings are defined in char-def.lua.

triangle is defined as a mathord (like nabla) while bigtriangleup is a mathop (like triangledown).

Sorry, bigtriangleup is a mathbin. (As I said, I don't understand how the mathclass of different triangle operators is determined). Aditya

Hi, The \triangle operator is used for instance in the « symmetric difference » of two subsets: if $E$ is a set and $A \subset E$, and $B \susbet E$, then one defines \startformula A \triangle B := (A \cup B) \setminus (A \cap B). \stopformula Then the mapping $(A,B) \mapsto A \triangle B$ is a commutative, associative binary operator on the subsets of $E$. Some people use instead $A \Delta B$, but this is not the traditional, nor the correct way, to write this « symmetric difference » of two sets. This is why, I guess, in TeX \triangle is an operator. I have seen also \triangledown as an operator, but I don’t recall the context in which it was used… Regarding the notation \nabla to denote the gradient, and \Delta, to denote the Laplace operator (which by the way can be defined as $\Delta u := \nabla \cdot (\nabla u)$), Mikael Sundqvist gave the correct observations. Best regards: OK On 11 avr. 2014, at 05:48, Aditya Mahajan wrote:

On Thu, 10 Apr 2014, Sanjoy Mahajan wrote:

...

Jannik,

You are right. \nabla looks much nicer and is placed correctly. (I still think the \triangledown placement is slightly off.)

My environment files from MkII days have \def\nabla{\triangledown}, so I never tried the true \nabla until your suggestion.

In MkIV: \triangledown is mapped to 0x25BD while nabla is mapped to 0x2207. These are different glyphs.

IIUC, the difference in placement is because \triangledown is defined as a mathop (and hence centered on the math-axis) while \nabla is defined as a mathord. Compare:

\startformula \nabla T \quad \triangledown T \quad \mathop{\nabla} T \stopformula

From what I remember, I was the one who added the mappings for triangledown as a mathop based on, I believe, unicode-math package in LaTeX. I don't understand what all the "triangle operators" are supposed to do. As such, I cannot say whether the wrong placement is due to the wrong font metrics or the wrong mapping (mathop vs mathord) by ConTeXt.

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On 4/13/2014 4:44 AM, Sanjoy Mahajan wrote:

Otared Kavian writes:

...

The \triangle operator is used for instance in the « symmetric difference » of two subsets

Ah, good to learn something about pure mathematics. In my mathematics degree, my tutor said, "You are very good at the applied material," which was not meant as a compliment.

So \triangle should be a \mathop rather than a \mathord? Right now, as Aditya pointed out, it's a \mathord ("ordinary"), in contrast to \bigtriangleup, which is the same character but typeset as a binary operator ("binary"). From char-def.lua :

[0x25B3]={ adobename="whiteuppointingtriangle", category="so", cjkwd="a", description="WHITE UP-POINTING TRIANGLE", direction="on", linebreak="ai", mathspec={ { class="ordinary", name="triangle", }, { class="binary", name="bigtriangleup", }, }, unicodeslot=0x25B3, },

I can change things but will only do that when all you mathematicians have some agreement about it ... Btw, it is still on my agenda to provide a mechanism for switching between math dictionaries (i.e. group symbols in group swith i fneeded different properties) so that one can switch between logic, statistics, streetfighting or whatever math. Hans ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | voip: 087 875 68 74 | www.pragma-ade.com | www.pragma-pod.nl -----------------------------------------------------------------

On 4/14/2014 11:30 AM, Sanjoy Mahajan wrote:

...

I can change things but will only do that when all you mathematicians have some agreement about it ...

Otared points out that the distinction between \triangle and \bigtriangleup comes from plain TeX. plain.tex has these definitions:

\mathchardef\triangle="0234 \mathchardef\bigtriangleup="2234

So \triangle is a math ord and \bigtriangleup a math bin.

For compatibility, that should probably stay true in ConTeXt too---even the low placement of \bigtriangledown, which I don't understand but which does reproduce plain TeX's placement.

why? if compatibility means 'not useable' we should fix it

...

Btw, it is still on my agenda to provide a mechanism for switching between math dictionaries (i.e. group symbols in group switch if needed different properties) so that one can switch between logic, statistics, streetfighting or whatever math.

Hm, like different dialects of a language. Plain TeX definitely speaks a pure-mathematician dialect. It would be interesting to see what symbol groups are useful in other dialects.

http://www.openmath.org/cdindex.html it would be interesting to come up with a reasonable list of math languages Hans ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | voip: 087 875 68 74 | www.pragma-ade.com | www.pragma-pod.nl -----------------------------------------------------------------

Dear List, If an article is "How about this?", in the bib list, it will be printed like author1, author2, ..., How about this?. Journal name... I am trying to remove "." after "?" From reading documents, I think I should change (bibl-apa) \insertarttitle{\bgroup }{\egroup. }{}% Right now it will add "." in all cases. Is it possible that I can change it to conditional statement. Something like if the original title ends with punctuation, do nothing, otherwise, add ".". Hope that I made myself clear. Thank you! Best, Peng