* atan2 function
@ 2022-10-13 5:40 Thangalin via ntg-context
2022-10-13 6:42 ` Max Chernoff via ntg-context
0 siblings, 1 reply; 13+ messages in thread
From: Thangalin via ntg-context @ 2022-10-13 5:40 UTC (permalink / raw)
To: mailing list for ConTeXt users; +Cc: Thangalin
Hi there,
How is atan2 called? I rolled my own as follows:
% SOT
\startuseMPgraphic{HexGridBaseGraphic}
vardef atantwo( expr ax, ay, bx, by ) =
save theta;
numeric dx;
numeric dy;
numeric theta;
dx := bx - ax;
dy := by - ay;
theta := 0;
if (dx > 0):
theta := atan( dy / dx );
elseif (dx < 0) and (dy >= 0):
theta := atan( dy / dx ) + pi;
elseif (dx < 0) and (dy < 0):
theta := atan( dy / dx ) - pi;
elseif (dx == 0) and (dy > 0):
theta := pi / 2;
elseif (dx == 0) and (dy < 0):
theta := -pi / 2;
fi;
%theta := atan( dy, dx );
theta
enddef;
% EOT
When this runs, the expected result is generated:
https://pdfhost.io/v/xdNxANU18_scaled
When uncommenting "atan( dy, dx )", an unexpected result is generated:
https://pdfhost.io/v/QdfU89IL._scaled
Is atan with two parameters supposed to behave like atan2?
Cheers!
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___________________________________________________________________________________
^ permalink raw reply [flat|nested] 13+ messages in thread* Re: atan2 function 2022-10-13 5:40 atan2 function Thangalin via ntg-context @ 2022-10-13 6:42 ` Max Chernoff via ntg-context 2022-10-13 19:51 ` Thangalin via ntg-context 0 siblings, 1 reply; 13+ messages in thread From: Max Chernoff via ntg-context @ 2022-10-13 6:42 UTC (permalink / raw) To: ntg-context; +Cc: Max Chernoff Hi, > How is atan2 called? I rolled my own as follows: > Is atan with two parameters supposed to behave like atan2? At mp-math.mpxl:167 there is: vardef atan primary x = angle(1,x) enddef ; The MetaPost manual says: The angle operator takes a pair and computes the two-argument arctangent; i.e., angle is the inverse of the dir operator So it looks like "angle" is the function that you want for "atan2". Thanks, -- Max ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context webpage : https://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : https://contextgarden.net ___________________________________________________________________________________ ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: atan2 function 2022-10-13 6:42 ` Max Chernoff via ntg-context @ 2022-10-13 19:51 ` Thangalin via ntg-context 2022-10-14 0:35 ` Max Chernoff via ntg-context 2022-10-14 12:26 ` Alan Braslau via ntg-context 0 siblings, 2 replies; 13+ messages in thread From: Thangalin via ntg-context @ 2022-10-13 19:51 UTC (permalink / raw) To: mailing list for ConTeXt users; +Cc: Thangalin Thank you, Max. The angle function doesn't appear to provide the same calculation as my atantwo in all cases. https://pdfhost.io/v/Oqj7XmibJ_scaled The shorter line segment should be directed towards the vertex closest to the longer line segment. I tried using both: theta := angle( dx, dy ); theta := angle( dy, dx ); Neither made a difference, in some cases the angle differs from what I'd expect. My implementation is based on the first version given here: https://en.wikipedia.org/wiki/Atan2#Definition_and_computation I have something that works, so this is more of a curiosity as to there being a difference between my implementation of atantwo and the angle function. Here's an example with many lines and the angle function: https://pdfhost.io/v/1T4jgBnxh_scaled On Wed, Oct 12, 2022 at 11:42 PM Max Chernoff <mseven@telus.net> wrote: > > Hi, > > > How is atan2 called? I rolled my own as follows: > > > Is atan with two parameters supposed to behave like atan2? > > At mp-math.mpxl:167 there is: > > vardef atan primary x = angle(1,x) enddef ; > > The MetaPost manual says: > > The angle operator takes a pair and computes the two-argument > arctangent; i.e., angle is the inverse of the dir operator > > So it looks like "angle" is the function that you want for "atan2". > > Thanks, > -- Max ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context webpage : https://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : https://contextgarden.net ___________________________________________________________________________________ ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: atan2 function 2022-10-13 19:51 ` Thangalin via ntg-context @ 2022-10-14 0:35 ` Max Chernoff via ntg-context 2022-10-14 8:07 ` Hans Hagen via ntg-context 2022-10-14 12:26 ` Alan Braslau via ntg-context 1 sibling, 1 reply; 13+ messages in thread From: Max Chernoff via ntg-context @ 2022-10-14 0:35 UTC (permalink / raw) To: ntg-context; +Cc: Max Chernoff Hi, > The angle function doesn't appear to provide the same calculation as > my atantwo in all cases. They both give the same results, but "angle" gives a result in degrees while "atantwo" gives a result in radians. This demo: \startMPpage vardef atantwo( expr dy, dx ) = save theta; numeric theta; theta := 0; if (dx > 0): theta := atan( dy / dx ); elseif (dx < 0) and (dy >= 0): theta := atan( dy / dx ) + pi; elseif (dx < 0) and (dy < 0): theta := atan( dy / dx ) - pi; elseif (dx == 0) and (dy > 0): theta := pi / 2; elseif (dx == 0) and (dy < 0): theta := -pi / 2; fi; theta enddef; def showangles(expr dx, dy) = message "---------------" message "atantwo " & decimal atantwo(dy, dx) message "angle " & decimal (angle(dx, dy) * pi / 180) message "angle " & decimal angle(dx, dy) message "(" & decimal dx & ", " & decimal dy & ")" enddef; showangles(1, 0); showangles(1, 1); showangles(0, 1); showangles(-1, 1); showangles(-1, 0); showangles(-1, -1); showangles(0, -1); showangles(1, -1); \stopMPpage gives: (1, 0) angle 0 angle 0 atantwo 0 --------------- (1, 1) angle 45 angle 0.78539816339744828 atantwo 0.78539816339744828 --------------- (0, 1) angle 90 angle 1.5707963267948966 atantwo 1.5707963267948966 --------------- (-1, 1) angle 135 angle 2.3561944901923448 atantwo 2.3561944901923448 --------------- (-1, 0) angle 180 angle 3.1415926535897931 atantwo 3.1415926535897931 --------------- (-1, -1) angle -135 angle -2.3561944901923448 atantwo -2.3561944901923448 --------------- (0, -1) angle -90 angle -1.5707963267948966 atantwo -1.5707963267948966 --------------- (1, -1) angle -45 angle -0.78539816339744828 atantwo -0.78539816339744828 --------------- Thanks, -- Max ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context webpage : https://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : https://contextgarden.net ___________________________________________________________________________________ ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: atan2 function 2022-10-14 0:35 ` Max Chernoff via ntg-context @ 2022-10-14 8:07 ` Hans Hagen via ntg-context 2022-10-14 14:40 ` Alan Braslau via ntg-context 0 siblings, 1 reply; 13+ messages in thread From: Hans Hagen via ntg-context @ 2022-10-14 8:07 UTC (permalink / raw) To: ntg-context; +Cc: Hans Hagen On 10/14/2022 2:35 AM, Max Chernoff via ntg-context wrote: > > Hi, > >> The angle function doesn't appear to provide the same calculation as >> my atantwo in all cases. > > They both give the same results, but "angle" gives a result in degrees > while "atantwo" gives a result in radians. This demo: > > \startMPpage > vardef atantwo( expr dy, dx ) = > save theta; > > numeric theta; > > theta := 0; > > if (dx > 0): > theta := atan( dy / dx ); > elseif (dx < 0) and (dy >= 0): > theta := atan( dy / dx ) + pi; > elseif (dx < 0) and (dy < 0): > theta := atan( dy / dx ) - pi; > elseif (dx == 0) and (dy > 0): > theta := pi / 2; > elseif (dx == 0) and (dy < 0): > theta := -pi / 2; > fi; > > theta > enddef; > > def showangles(expr dx, dy) = > message "---------------" > message "atantwo " & decimal atantwo(dy, dx) > message "angle " & decimal (angle(dx, dy) * pi / 180) > message "angle " & decimal angle(dx, dy) > message "(" & decimal dx & ", " & decimal dy & ")" > enddef; > > showangles(1, 0); > showangles(1, 1); > showangles(0, 1); > showangles(-1, 1); > showangles(-1, 0); > showangles(-1, -1); > showangles(0, -1); > showangles(1, -1); > \stopMPpage So you suggest to add atantwo? As side note, you can redure your definition to: vardef atantwo( expr dy, dx ) = if (dx > 0): atan( dy / dx ) elseif (dx < 0) and (dy >= 0): atan( dy / dx ) + pi elseif (dx < 0) and (dy < 0): atan( dy / dx ) - pi elseif (dx == 0) and (dy > 0): pi / 2 elseif (dx == 0) and (dy < 0): -pi / 2 else : 0 fi enddef ; and then vardef atantwo(expr dy, dx) = if dx == 0 : if dy < 0 : - fi pi / 2 else : atan(dy/dx) if dx > 0 : if dy < 0 : - else : + fi pi fi fi enddef ; going further makes us end up in an one-line obscurity Hans ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl ----------------------------------------------------------------- ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context webpage : https://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : https://contextgarden.net ___________________________________________________________________________________ ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: atan2 function 2022-10-14 8:07 ` Hans Hagen via ntg-context @ 2022-10-14 14:40 ` Alan Braslau via ntg-context 2022-10-14 18:59 ` Thangalin via ntg-context 0 siblings, 1 reply; 13+ messages in thread From: Alan Braslau via ntg-context @ 2022-10-14 14:40 UTC (permalink / raw) To: Hans Hagen via ntg-context; +Cc: Alan Braslau On Fri, 14 Oct 2022 10:07:19 +0200 Hans Hagen via ntg-context <ntg-context@ntg.nl> wrote: > So you suggest to add atantwo? As side note, you can redure your > definition to: > > vardef atantwo(expr dy, dx) = > if dx == 0 : > if dy < 0 : - fi pi / 2 > else : > atan(dy/dx) if dx > 0 : if dy < 0 : - else : + fi pi fi > fi > enddef ; > > going further makes us end up in an one-line obscurity An absurdity, as further discussion on this thread has shown: atan is derived from angle, which is essentially atan2. There is no need to circle around. As a side point, I now use MP doubleprecision mode by default, although I do believe that it is still preferable to use classic scaled integer mode (and minifun) for text graphical embellishments. The only practical point to consider when using doubleprecision mode for me is the need to explicitly use format with "decimal i" to round the text rendering of numbers. Alan ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context webpage : https://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : https://contextgarden.net ___________________________________________________________________________________ ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: atan2 function 2022-10-14 14:40 ` Alan Braslau via ntg-context @ 2022-10-14 18:59 ` Thangalin via ntg-context 2022-10-14 22:42 ` Alan Braslau via ntg-context 0 siblings, 1 reply; 13+ messages in thread From: Thangalin via ntg-context @ 2022-10-14 18:59 UTC (permalink / raw) To: mailing list for ConTeXt users; +Cc: Thangalin I don't think an atantwo is needed. I *thought* I had read somewhere that atan( y, x ) was equivalent to calling atan2 in Lua. Ensuring there's no breakage when x == y would be nice, though. It was a little surprising to see angle return degrees rather than radians, but it does simplify my code: dc := vbc - vac; dr := vbr - var; vi := 0; if not( dc == dr ): vi := round( angle( dc, dr ) / 60 ); fi; % Compute the direction towards the first segment (to vertex of an edge). vangle := vi * 60 * pi / 180; Even simpler would be: dc := vbc - vac; dr := vbr - var; vi := round( angle( dc, dr ) / 60 ); % returns 0 when dc == dr % Compute the direction towards the first segment (to vertex of an edge). vangle := vi * 60 * pi / 180; Or accepting a third argument as the return value in the special case: vi := round( angle( dc, dr, 0 ) / 60 ); % returns 0 when dc == dr Cheers! ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context webpage : https://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : https://contextgarden.net ___________________________________________________________________________________ ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: atan2 function 2022-10-14 18:59 ` Thangalin via ntg-context @ 2022-10-14 22:42 ` Alan Braslau via ntg-context 2022-10-14 23:09 ` Thangalin via ntg-context 0 siblings, 1 reply; 13+ messages in thread From: Alan Braslau via ntg-context @ 2022-10-14 22:42 UTC (permalink / raw) To: Thangalin; +Cc: Alan Braslau, mailing list for ConTeXt users On Fri, 14 Oct 2022 11:59:49 -0700 Thangalin <thangalin@gmail.com> wrote: > I don't think an atantwo is needed. I *thought* I had read somewhere > that atan( y, x ) was equivalent to calling atan2 in Lua. Ensuring > there's no breakage when x == y would be nice, though. It was a little > surprising to see angle return degrees rather than radians, but it > does simplify my code: > > dc := vbc - vac; > dr := vbr - var; > vi := 0; > > if not( dc == dr ): > vi := round( angle( dc, dr ) / 60 ); > fi; > > % Compute the direction towards the first segment (to vertex of > an edge). vangle := vi * 60 * pi / 180; > > Even simpler would be: > > dc := vbc - vac; > dr := vbr - var; > vi := round( angle( dc, dr ) / 60 ); % returns 0 when dc == dr > > % Compute the direction towards the first segment (to vertex of > an edge). vangle := vi * 60 * pi / 180; > > Or accepting a third argument as the return value in the special case: > > vi := round( angle( dc, dr, 0 ) / 60 ); % returns 0 when dc == > dr > > Cheers! vi := if (dc = dr) : 0 else : round (angle(dc,dr)/60) fi ; Alan ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context webpage : https://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : https://contextgarden.net ___________________________________________________________________________________ ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: atan2 function 2022-10-14 22:42 ` Alan Braslau via ntg-context @ 2022-10-14 23:09 ` Thangalin via ntg-context 2022-10-15 1:22 ` Alan Braslau via ntg-context 0 siblings, 1 reply; 13+ messages in thread From: Thangalin via ntg-context @ 2022-10-14 23:09 UTC (permalink / raw) To: Alan Braslau; +Cc: Thangalin, mailing list for ConTeXt users That's certainly tighter, thank you, Alan. Would making the conditional part of the API be useful to others? Cheers! On Fri, Oct 14, 2022 at 3:42 PM Alan Braslau <alan.braslau@icloud.com> wrote: > > On Fri, 14 Oct 2022 11:59:49 -0700 > Thangalin <thangalin@gmail.com> wrote: > > > I don't think an atantwo is needed. I *thought* I had read somewhere > > that atan( y, x ) was equivalent to calling atan2 in Lua. Ensuring > > there's no breakage when x == y would be nice, though. It was a little > > surprising to see angle return degrees rather than radians, but it > > does simplify my code: > > > > dc := vbc - vac; > > dr := vbr - var; > > vi := 0; > > > > if not( dc == dr ): > > vi := round( angle( dc, dr ) / 60 ); > > fi; > > > > % Compute the direction towards the first segment (to vertex of > > an edge). vangle := vi * 60 * pi / 180; > > > > Even simpler would be: > > > > dc := vbc - vac; > > dr := vbr - var; > > vi := round( angle( dc, dr ) / 60 ); % returns 0 when dc == dr > > > > % Compute the direction towards the first segment (to vertex of > > an edge). vangle := vi * 60 * pi / 180; > > > > Or accepting a third argument as the return value in the special case: > > > > vi := round( angle( dc, dr, 0 ) / 60 ); % returns 0 when dc == > > dr > > > > Cheers! > > vi := if (dc = dr) : 0 else : round (angle(dc,dr)/60) fi ; > > Alan ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context webpage : https://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : https://contextgarden.net ___________________________________________________________________________________ ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: atan2 function 2022-10-14 23:09 ` Thangalin via ntg-context @ 2022-10-15 1:22 ` Alan Braslau via ntg-context 0 siblings, 0 replies; 13+ messages in thread From: Alan Braslau via ntg-context @ 2022-10-15 1:22 UTC (permalink / raw) To: Thangalin; +Cc: Alan Braslau, mailing list for ConTeXt users On Fri, 14 Oct 2022 16:09:41 -0700 Thangalin <thangalin@gmail.com> wrote: > Would making the conditional part of the API be useful to others? Of course, $\tan^{-1}(\pm 1)$ is undefined (mathematically). Alan ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context webpage : https://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : https://contextgarden.net ___________________________________________________________________________________ ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: atan2 function 2022-10-13 19:51 ` Thangalin via ntg-context 2022-10-14 0:35 ` Max Chernoff via ntg-context @ 2022-10-14 12:26 ` Alan Braslau via ntg-context 2022-10-14 12:58 ` Taco Hoekwater via ntg-context 1 sibling, 1 reply; 13+ messages in thread From: Alan Braslau via ntg-context @ 2022-10-14 12:26 UTC (permalink / raw) To: mailing list for ConTeXt users; +Cc: Alan Braslau Are you using MP in scaled integer or in doubleprecision mode? I have not looked into the MP angle operator code, but my suspicion is that it is based on some super-clever John Hobby scheme optimized for scaled integer calculations. Hans has integrated the entire math library (and more) into lmtx. On 13/10/22 13/10/22, 13:51, Thangalin via ntg-context wrote: > Thank you, Max. > > The angle function doesn't appear to provide the same calculation as > my atantwo in all cases. > > https://pdfhost.io/v/Oqj7XmibJ_scaled > > The shorter line segment should be directed towards the vertex closest > to the longer line segment. I tried using both: > > theta := angle( dx, dy ); > theta := angle( dy, dx ); > > Neither made a difference, in some cases the angle differs from what I'd expect. > > My implementation is based on the first version given here: > > https://en.wikipedia.org/wiki/Atan2#Definition_and_computation > > I have something that works, so this is more of a curiosity as to > there being a difference between my implementation of atantwo and the > angle function. > > Here's an example with many lines and the angle function: > https://pdfhost.io/v/1T4jgBnxh_scaled > > On Wed, Oct 12, 2022 at 11:42 PM Max Chernoff <mseven@telus.net> wrote: >> >> Hi, >> >>> How is atan2 called? I rolled my own as follows: >> >>> Is atan with two parameters supposed to behave like atan2? >> >> At mp-math.mpxl:167 there is: >> >> vardef atan primary x = angle(1,x) enddef ; >> >> The MetaPost manual says: >> >> The angle operator takes a pair and computes the two-argument >> arctangent; i.e., angle is the inverse of the dir operator >> >> So it looks like "angle" is the function that you want for "atan2". >> >> Thanks, >> -- Max > ___________________________________________________________________________________ > If your question is of interest to others as well, please add an entry to the Wiki! > > maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context > webpage : https://www.pragma-ade.nl / http://context.aanhet.net > archive : https://bitbucket.org/phg/context-mirror/commits/ > wiki : https://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://www.ntg.nl/mailman/listinfo/ntg-context webpage : https://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : https://contextgarden.net ___________________________________________________________________________________ ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: atan2 function 2022-10-14 12:26 ` Alan Braslau via ntg-context @ 2022-10-14 12:58 ` Taco Hoekwater via ntg-context 2022-10-14 13:05 ` luigi scarso via ntg-context 0 siblings, 1 reply; 13+ messages in thread From: Taco Hoekwater via ntg-context @ 2022-10-14 12:58 UTC (permalink / raw) To: mailing list for ConTeXt users; +Cc: Taco Hoekwater > On 14 Oct 2022, at 14:26, Alan Braslau via ntg-context <ntg-context@ntg.nl> wrote: > > Are you using MP in scaled integer or in doubleprecision mode? > > I have not looked into the MP angle operator code, but my suspicion is that it is based on some super-clever John Hobby scheme optimized for scaled integer calculations. The scaled version of “angle” is a handwritten approximation in web, not using any math library. I really doubt that that code is faster than calling atan2() on a modern machine, but I’ve kept it in because using a lib might give slightly different results. The double version of “angle" uses atan2() internally already, so that the atantwo macro is just duplicating the internals for that case. The decimal version of “angle’ uses a dedicated decNumberAtan2() library call. > > Hans has integrated the entire math library (and more) into lmtx. > > On 13/10/22 13/10/22, 13:51, Thangalin via ntg-context wrote: >> Thank you, Max. >> The angle function doesn't appear to provide the same calculation as >> my atantwo in all cases. >> https://pdfhost.io/v/Oqj7XmibJ_scaled >> The shorter line segment should be directed towards the vertex closest >> to the longer line segment. I tried using both: >> theta := angle( dx, dy ); >> theta := angle( dy, dx ); >> Neither made a difference, in some cases the angle differs from what I'd expect. >> My implementation is based on the first version given here: >> https://en.wikipedia.org/wiki/Atan2#Definition_and_computation >> I have something that works, so this is more of a curiosity as to >> there being a difference between my implementation of atantwo and the >> angle function. >> Here's an example with many lines and the angle function: >> https://pdfhost.io/v/1T4jgBnxh_scaled >> On Wed, Oct 12, 2022 at 11:42 PM Max Chernoff <mseven@telus.net> wrote: >>> >>> Hi, >>> >>>> How is atan2 called? I rolled my own as follows: >>> >>>> Is atan with two parameters supposed to behave like atan2? >>> >>> At mp-math.mpxl:167 there is: >>> >>> vardef atan primary x = angle(1,x) enddef ; >>> >>> The MetaPost manual says: >>> >>> The angle operator takes a pair and computes the two-argument >>> arctangent; i.e., angle is the inverse of the dir operator >>> >>> So it looks like "angle" is the function that you want for "atan2". >>> >>> Thanks, >>> -- Max >> ___________________________________________________________________________________ >> If your question is of interest to others as well, please add an entry to the Wiki! >> maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context >> webpage : https://www.pragma-ade.nl / http://context.aanhet.net >> archive : https://bitbucket.org/phg/context-mirror/commits/ >> wiki : https://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://www.ntg.nl/mailman/listinfo/ntg-context > webpage : https://www.pragma-ade.nl / http://context.aanhet.net > archive : https://bitbucket.org/phg/context-mirror/commits/ > wiki : https://contextgarden.net > ___________________________________________________________________________________ — Taco Hoekwater E: taco@bittext.nl genderfluid (all pronouns) ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context webpage : https://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : https://contextgarden.net ___________________________________________________________________________________ ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: atan2 function 2022-10-14 12:58 ` Taco Hoekwater via ntg-context @ 2022-10-14 13:05 ` luigi scarso via ntg-context 0 siblings, 0 replies; 13+ messages in thread From: luigi scarso via ntg-context @ 2022-10-14 13:05 UTC (permalink / raw) To: mailing list for ConTeXt users; +Cc: luigi scarso [-- Attachment #1.1: Type: text/plain, Size: 889 bytes --] On Fri, 14 Oct 2022 at 14:58, Taco Hoekwater via ntg-context < ntg-context@ntg.nl> wrote: > > > > On 14 Oct 2022, at 14:26, Alan Braslau via ntg-context < > ntg-context@ntg.nl> wrote: > > > > Are you using MP in scaled integer or in doubleprecision mode? > > > > I have not looked into the MP angle operator code, but my suspicion is > that it is based on some super-clever John Hobby scheme optimized for > scaled integer calculations. > > The scaled version of “angle” is a handwritten approximation in web, not > using > any math library. I really doubt that that code is faster than calling > atan2() > on a modern machine, but I’ve kept it in because using a lib might give > slightly > different results. > iirc, in metapost the whole scaled number system has no dependency from any external math library (I have not checked the lmtx source yet). [-- Attachment #1.2: Type: text/html, Size: 1335 bytes --] [-- Attachment #2: Type: text/plain, Size: 496 bytes --] ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context webpage : https://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : https://contextgarden.net ___________________________________________________________________________________ ^ permalink raw reply [flat|nested] 13+ messages in thread
end of thread, other threads:[~2022-10-15 1:22 UTC | newest] Thread overview: 13+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2022-10-13 5:40 atan2 function Thangalin via ntg-context 2022-10-13 6:42 ` Max Chernoff via ntg-context 2022-10-13 19:51 ` Thangalin via ntg-context 2022-10-14 0:35 ` Max Chernoff via ntg-context 2022-10-14 8:07 ` Hans Hagen via ntg-context 2022-10-14 14:40 ` Alan Braslau via ntg-context 2022-10-14 18:59 ` Thangalin via ntg-context 2022-10-14 22:42 ` Alan Braslau via ntg-context 2022-10-14 23:09 ` Thangalin via ntg-context 2022-10-15 1:22 ` Alan Braslau via ntg-context 2022-10-14 12:26 ` Alan Braslau via ntg-context 2022-10-14 12:58 ` Taco Hoekwater via ntg-context 2022-10-14 13:05 ` luigi scarso via ntg-context
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