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
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