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% magneticflux.mp
% L. Nobre G.
% IYP (2005)
%input featpost3Dplus2D;
verbatimtex
\documentclass{article}
\usepackage{palatino,mathpazo}
\begin{document}
etex
TDAtiplen := 0.1; % tdarrow
TDAhalftipbase := 0.04; % Three-Dimensional
TDAhalfthick := 0.02; % Arrow
ForePen := pencircle scaled 10pt;
BackPen := pencircle scaled 6pt;
numeric ranga;
ranga = 30+uniformdeviate(120);
def ellip( expr TheVal ) =
( (cosd(360*TheVal),sind(360*TheVal)/sind(ranga),0) )
enddef;
beginfig(2);
f := ( 4, 1, 2 );
Spread := 90;
pen blackpen, whitepen;
numeric majoraxe, i, j, gridstepn, gridstep, gridstart, halen, rang;
numeric ellfocus, totdist, marginl;
path espira, partes, covere;
color avec, midvec;
halen = 1;
marginl = 0.14;
rang = 45+30*floor(uniformdeviate(3.9));
show rang;
avec = (0,cosd(rang),sind(rang))*halen;
blackpen = pencircle scaled 5pt;
whitepen = pencircle scaled 3pt;
majoraxe = 1.2 + uniformdeviate(0.8);
ellfocus = majoraxe +-+ 1;
gridstepn= 15;
gridstep = 2*majoraxe/(gridstepn-1);
gridstart= 0.5*gridstepn*gridstep;
espira = ellipticpath( black, -red, -green*majoraxe );
draw espira withpen blackpen;
undraw espira withpen whitepen;
for j=-1 step gridstep until 1:
for i=-gridstart step gridstep until gridstart:
midvec := (j,i,0);
totdist := conorm(midvec-(0,-ellfocus,0))+conorm(midvec-(0,ellfocus,0));
if 2*majoraxe-marginl > totdist:
tdarrow( midvec, midvec+avec );
% draw rp(midvec) withpen whitepen;
fi;
endfor;
endfor;
partes = subpath (10.3,25.6) of espira;
covere = subpath (10,26) of espira;
draw partes withpen blackpen;
undraw covere withpen whitepen;
endfig;
beginfig(1);
f := ( 4, 1.9, 1.22 );
Spread := 90;
numeric nodc, lsc;
nodc = 10;
lsc = 2.4;
closedline( true, 200, 0.5, 1.75 )( ellip );
numeric i, j, circlesize, polar, phi;
color currpos, ini, fin, avec;
string comm;
avec = (0,cosd(ranga),sind(ranga));
circlesize = 1.86/nodc;
for i=0.93 step -circlesize until 0.4*circlesize:
polar := floor(6.28318*i/circlesize);
for j=1 upto polar:
phi := 360*j/polar;
currpos := i*(cosd(phi),sind(phi)/sind(ranga),0);
comm:="tdarrow("
& cstr( currpos )
& ","
& cstr( currpos + avec )
& ");";
getready( comm, currpos );
endfor;
endfor;
doitnow;
pickup pencircle scaled 2pt;
drawarrow rp((0,1.07/sind(ranga),0))--rp((0,2.47,0));
drawarrow rp((1.07,0,0))--rp((1.67,0,0));
angline((0,2.37,0),(0,0.93/sind(ranga),0)+avec,(0,0.93/sind(ranga),0),
0.3, btex $\alpha$ etex scaled lsc, urt);
label.bot( btex $x$ etex scaled lsc, rp((1.67,0,0)) );
label.bot( btex $y$ etex scaled lsc, rp((0,2.47,0)) );
endfig;
verbatimtex
\end{document}
etex
end.
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