On Mon, 8 Oct 2018 16:00:10 -0400 (EDT)
Aditya Mahajan <adit...@umich.edu> wrote:
> On Sun, 7 Oct 2018, Hans Hagen wrote:
>
> > On 10/7/2018 7:14 PM, Alan Braslau wrote:
> >> On Sun, 7 Oct 2018 17:25:35 +0200
> >> "Mikael P. Sundqvist" <mic...@gmail.com> wrote:
> >>
> >>> ContourPlot[2 x^5 + x y + y^5 == 0, {x, 0, 2}, {y, -2, 1/2}]
> >>
> >> Brut force:
> >> [...]
> >>
> > as this takes some time here's a cheat:
> >
> > \starttext
> >
> > \startbuffer[demo]
> > [...]
> > \stopbuffer
> >
> > \startTEXpage
> > \typesetbuffer[demo]
> > \stopTEXpage
> > \stoptext
> >
> > a next run the already prepared buffer will be taken unles it has been
> > changed.
>
> I thought that this will also be a good usecase of showing Lua+MP
> interaction. I wrote the code below following the metafun manual, but I cannot
> get it to compile. What am I missing?
>
>
> \startluacode
> local f = function(x, y) return 2*x^5 + x*y + y^5 end
> local abs = math.abs
>
> contour = { }
>
> function contour.generate(x_min, x_max, y_min, y_max)
> local pts = { }
> local length = 1000
> local eps = 1e-3
>
> for xi = x_min, x_max, (x_max - x_min)/length do
> for yi = y_min, y_max, (y_max - y_min)/length do
> if abs(f(xi,yi)) < eps then
> pts[#pts + 1] = {xi, yi}
> end
> end
> end
>
> return pts
> end
>
> contour.data = contour.generate(0, 2, -1, 0.5)
>
> function contour.n()
> mp.print(#contour.data)
> end
>
> function contour.point(i)
> mp.pair(contour.data[i])
> end
>
> \stopluacode
>
> \starttext
> \startMPpage[instance=doublefun]
> pen savedpen ; savedpen := currentpen ;
> pickup pencircle scaled .01 ;
>
> p := for i = 1 upto lua.contour.n() :
> lua.contour.point(i) ..
> endfor cycle;
>
> draw subpath (0,length p - 1) of p ;
> setbounds currentpicture to (0,-2)--(2,-2)--(2,.5)--(0,.5)--cycle ;
> currentpicture := currentpicture xsized 5cm ;
> pickup savedpen ;
> picture pic ; pic := currentpicture ;
> drawarrow llcorner pic--lrcorner pic ;
> drawarrow llcorner pic--ulcorner pic ;
> label.rt ("$x$", lrcorner pic) ;
> label.top("$y$", ulcorner pic) ;
> for x=0 step .5 until 2 :
> label.bot(decimal x,(x/2)[llcorner pic,lrcorner pic]) ;
> endfor ;
> for y=0 step .5 until 2.5 :
> label.lft(decimal (y-2),(y/2.5)[llcorner pic,ulcorner pic]) ;
> endfor ;
> \stopMPpage
> \stoptext
>
>
> I get an error:
>
>
> ! Missing argument to lua.
> <to be read again>
> contour
> <*> ...caled .01 ; p := for i = 1 upto lua.contour
> .n() : lua.contour.point(i...
> That macro has more parameters than you thought.
> I'll continue by pretending that each missing argument
> is either zero or null.
>
>
> Thanks,
> Aditya
You need to put it into the mp namespace:
(then eps should be made a linear function of xi)
(and, indeed this is much faster than calculating in MP)
Alan
\startluacode
local f = function(x, y) return 2*x^5 + x*y + y^5 end
local abs = math.abs
local contour = { }
function contour.generate(x_min, x_max, y_min, y_max)
local pts = { }
local length = 1000
local eps = 1e-3
local n = 0
for xi = x_min, x_max, (x_max - x_min)/length do
for yi = y_min, y_max, (y_max - y_min)/length do
if abs(f(xi,yi)) < eps then
n = n + 1
pts[n] = {xi, yi}
end
end
end
return pts
end
contour.data = contour.generate(0, 2, -1, 0.5)
function mp.ContourN()
mp.print(#contour.data)
end
function mp.ContourPoint(i)
mp.pair(contour.data[i])
end
function mp.ContourPath()
mp.path(contour.data)
end
\stopluacode
\starttext
\startMPpage[instance=doublefun]
draw lua.mp.ContourPath() withpen pencircle scaled .01 ;
setbounds currentpicture to (0,-2)--(2,-2)--(2,.5)--(0,.5)--cycle ;
currentpicture := currentpicture xsized 5cm ;
picture pic ; pic := currentpicture ;
drawarrow llcorner pic--lrcorner pic ;
drawarrow llcorner pic--ulcorner pic ;
label.rt ("$x$", lrcorner pic) ;
label.top("$y$", ulcorner pic) ;
for x=0 step .5 until 2 :
label.bot(decimal x,(x/2)[llcorner pic,lrcorner pic]) ;
endfor ;
for y=0 step .5 until 2.5 :
label.lft(decimal (y-2),(y/2.5)[llcorner pic,ulcorner pic]) ;
endfor ;
\stopMPpage
\stoptext
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