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% trajectoryline.mp
% L. Nobre G.
% 2003
%input featpost3Dplus2D;
Spread := 30;
f := (10,0,0);
color posa, posb, axer;
numeric kfac, refrad;
posa = -5*green;
posb = 5*green;
axer = blue;
kfac = 2.5;
refrad = 1;
def vecfunc( expr posit )=
begingroup
save modula, modulb, field;
color field;
numeric modula, modulb;
modula = conorm( posit-posa );
modulb = conorm( posit-posb );
field = ( posit-posa )/(modula**3)+kfac*( posit-posb )/(modulb**3);
( -field )
endgroup
enddef;
def magfunc( expr posit )=
begingroup
save perpd, refvec, dist;
color perpd, refvec;
numeric dist;
perpd = ccrossprod( axer, posit );
refvec = posit - refrad*ncrossprod( perpd, axer );
dist = conorm( refvec );
( ncrossprod( refvec, perpd )/(dist**2) )
endgroup
enddef;
beginfig(1);
numeric i, lena, numa, sa, diffstep, ray;
color stp, svl;
path oneline;
pen grossa, fina;
grossa = pencircle scaled 3pt;
fina = pencircle scaled 2pt;
lena = 400;
numa = 58;
diffstep = 0.12;
ray = 3.5;
sa = 168;
for i=sa step numa until (180):
stp := ( 0, ray*cosd(i), ray*sind(i) );
svl := N( -stp );
oneline := trajectorypath( lena, stp, svl, diffstep, vecfunc );
draw oneline withpen grossa;
draw oneline withpen fina withcolor background;
endfor;
draw rp(posa) withpen grossa;
draw rp(posb) withpen grossa;
endfig;
beginfig(2);
numeric i, lena, numa, sa, diffstep, ray;
color stp, svl;
path oneline;
pen grossa, fina;
grossa = pencircle scaled 3pt;
fina = pencircle scaled 2pt;
lena = 100;
numa = 4;
diffstep = 1;
ray = 5.5;
sa = 97;
for i=sa step numa until (120):
stp := ( 0, ray*cosd(i), ray*sind(i) );
svl := 0.8*N( -stp );
oneline := magnetictrajectorypath( lena, stp, svl, diffstep, magfunc );
draw oneline withpen grossa;
draw oneline withpen fina withcolor background;
endfor;
draw rp(black) withpen grossa;
endfig;
end.
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