This short article (being far from complete) is about Math and arrows used for vectors, as in <context>$\overrightarrow{AB}$</context>. If anyone feels like writing a more extensive article about math arrows in general, you're wellcome to do so. == Vectors with arrows == === \vec, <context>$\vec{\strut}$</context> === The simplest way to write vectors is to use <code>\vec</code>:<context source="yes">$(\vec{\imath}, \vec{\jmath}, \vec{k})$</context> However, that solution is not applicable when one needs to use longer arrows, as in: <context source="yes">$\vec{AB}$</context> === \overrightarrow, <context>$\overrightarrow{\strut}$</context> === For such cases, the plain format provides another command, \overrightarrow: <context source="yes">$\overrightarrow{AB}$</context> Hovever, again, that command seems to be unsuitable for short letters:<context source="yes">$(\overrightarrow{\imath}, \overrightarrow{\jmath}, \overrightarrow{k})$</context> which means that one would need to combine both commands at best. Another nasty property of \overrightarrow is that it doesn't scale down (textstyle, scriptstyle, ...): <context source="yes">$(X_{Y_{AB}}, X_{Y_{\overrightarrow{AB}}})$</context> ''Wait a minute ... has it really been fixed in ConTeXt when compared moved to plain TeX ???That's not fair! I cannot demonstrate the problem now! ''-- [[User:Mojca Miklavec|Mojca]] (crying) Anyway, here's how it looks like in plain TeX: <context>$(X_{Y_{AB}}, X_{Y_{\displaystyle{\overrightarrow{AB}}}})$<Math/context> == Vectors with harpoons == In some countries vectors are written with harpoons as opposed to arrows. Plain TeX has no support for that, add to that the fact that fonts have no suitable glyphs. {{todo|clean the code (some might be in the core already), describe Aditya's macros}} <context>\unprotect \def\mtharrowfill#1#2#3#4#5#6#7#8% AM: Added #8 (for displaystyle) {$\mathsurround 0pt \thickmuskip0mu\medmuskip\thickmuskip\thinmuskip\thickmuskip \relax#8#5% \mkern-#1mu \cleaders\hbox{$#8\mkern -#2mu#6\mkern -#3mu$}\hfill \mkern-#4mu#7$} %D Now we need to make sure that the extensible arrows do not get%D %D affected. So... \def\domthxarr#1#2#3#4#5% hm, looks like we do a double mathrel {\begingroup \def\mtharrfactor{1}% \def\mtharrextra {0}% \processaction[#1] % will be sped up [ \v!none=>\def\mtharrfactor{0}, \v!small=>\def\mtharrextra{10}, \v!medium=>\def\mtharrextra{15}, \v!big=>\def\mtharrextra{20}, \v!normal=>, \v!default=>, \v!unknown=>\doifnumberelse{#1}{\def\mtharrextra{#1}}\donothing]% \mathsurround\zeropoint \muskip0=\thirdoffourarguments #2mu \muskip2=\fourthoffourarguments #2mu \muskip4=\firstoffourarguments #2mu \muskip6=\secondoffourarguments #2mu \muskip0=\mtharrfactor\muskip0 \advance\muskip0 \mtharrextra mu \muskip2=\mtharrfactor\muskip2 \advance\muskip2 \mtharrextra mu \setbox0\hbox{$\scriptstyle \mkern\muskip4\relax \mkern\muskip0\relax #5\relax \mkern\muskip2\relax \mkern\muskip6\relax $}% \setbox4\hbox{#3\displaystyle}% AM: Added displaystyle \dimen0\wd0 \ifdim\wd4>\dimen0 \dimen0\wd4 \fi \setbox2\hbox{$\scriptstyle \mkern\muskip4\relax \mkern\muskip0\relax #4\relax \mkern\muskip2\relax \mkern\muskip6\relax $}% \ifdim\wd2>\dimen0 \dimen0\wd2 \fi \setbox4\hbox to \dimen0{#3\displaystyle}% AM: added dislaystyle \mathrel{\mathop{\hbox to\dimen0{\hss\copy4\hss}}\limits^{\box0}_{\box2}} \endgroup} \let\domthxarrsingle\domthxarr %D Now, for defining overarrows. \def\definemathoverarrow {\dotripleargument\dodefinemathoverarrow} \def\dodefinemathoverarrow[#1][#2][#3]% {\ifthirdargument \setvalue{#1}{\dohandlemathoverarrow[#2][#3]}% \else \setvalue{#1}{\dohandlemathoverarrow[\zeropoint][#2]}% \fi} \def\dohandlemathoverarrow[#1][#2]% {\mathpalette{\dodohanglemathoverarrow{#1}{#2}}} % Note: math-pln has \kern-\onepoint, amsmath does not. I keep the% % kern amount as an option. This is useful with overharpoons. \def\dodohanglemathoverarrow#1#2#3#4% {\vbox{\ialign{##\crcr #2#3\crcr \noalign{\kern#1\nointerlineskip} $\m@th\hfil#3#4\hfil$\crcr}}} \protect \definemathoverarrow [overleftarrow] [\leftarrowfill]\definemathoverarrow [overrightarrow] [\rightarrowfill]\definemathoverarrow [overleftrightarrow] [\leftrightarrowfill] %$\overleftarrow{A}$ $\overleftarrow{ABC}$%$a_{\overleftarrow{A}}$ $b_{\overleftarrow{ABC}}$%%$\overleftrightarrow{A}$ $\overleftrightarrow{ABC}$%%$a_{\overleftrightarrow{A}}$ $b_{\overleftrightarrow{ABC}}$ \definemathoverarrow [overtwoheadrightarrow] [\twoheadrightarrowfill]\definemathoverarrow [overtwoheadleftarrow] [\twoheadleftarrowfill]\definemathoverarrow [overrightharpoondown] [1pt] [\rightharpoondownfill]\definemathoverarrow [overrightharpoonup] [\rightharpoonupfill]\definemathoverarrow [overleftharpoondown] [1pt] [\leftharpoondownfill]\definemathoverarrow [overleftharpoonup] [\leftharpoonupfill] \def\definemathshortarrow {\dotripleargument\dodefinemathshortarrow} \def\dodefinemathshortarrow[#1][#2][#3]% {\ifthirdargument \setvalue{#1}{\dohandlemathshortarrow[#2][#3]}% \else \setvalue{#1}{\dohandlemathshortarrow[\zeropoint][#2]}% \fi} \def\dohandlemathshortarrow[#1][#2]% {\mathpalette{\dodohandlemathshortarrow{#1}{#2}}} \def\dodohandlemathshortarrow#1#2#3#4% {\setbox0\hbox{$\m@th#3#4$}% \vbox{\ialign{##\crcr \mirror{\clip[width=\wd0]{\mirror{$\m@th#2#3$}}}\crcr \noalign{\kern#1\nointerlineskip}% $\m@th\hfil#3#4\hfil$\crcr}}} \definemathshortarrow [shortoverrightharpoonup] [\rightharpoonup] \let\myvec\shortoverrightharpoonup$(\myvec{\imath},\myvec{\jmath},\myvec{k})$ or $\myvec{\nabla}$, $\myvec{\sigma}$, $\myvec{r}$ or $\displaystyle{A^{\myvec{ABCD}}}$</context> === \overrightharpoonup, <context>$\rightharpoonup$</context> === {{todo|compare sizes of different arrows}} == Antykwa Toruńska == {{todo|Jacko and Janusz have added some extra glyphs - explore, describe the problem & solution and draw}} \mathchardef\minusleft="32C9 \mathchardef\minusright="32CA \mathchardef\minusc="32C8 == See also == This is a [[This Way - My Way#MyWay|My Way]] about a related topic:* [http://dl.contextgarden.net/myway/matharrows.pdf Extensible Arrows in ConTeXt] by Aditya Mahajan [[Category:Math]]