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% fieldlinesnorma.mp
% L. Nobre G.
% 2003
input featpost3Dplus2D;
Spread := 25;
f := (10,-2,7);
color posa, posb, perpd;
numeric kfac;
posa = -5*green;
posb = 5*green;
perpd = (1,0,1);
kfac = -10;
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);
( N(field) )
endgroup
enddef;
def potfunc( expr posit )=
begingroup
save field;
color field;
field = vecfunc( posit );
( ncrossprod( field, perpd ) )
endgroup
enddef;
beginfig(1);
numeric i, lena, lenb, numa, numb, sa, sb, diffstep, ray;
color stp;
path oneline;
pen grossa, fina;
grossa = pencircle scaled 3pt;
fina = pencircle scaled 2pt;
lena = 85;
lenb = 20;
numa = 30;
numb = 18;
diffstep = 0.1;
ray = 0.5;
sa = 75;
sb = 90;
for i=sa step numa until (360+sa):
stp := posa+( ray*cosd(i), ray*sind(i), 0 );
oneline := fieldlinepath( lena, stp, diffstep, vecfunc );
draw oneline withpen grossa;
% draw oneline withpen fina withcolor background;
endfor;
for i=sb step numb until (360+sb):
stp := posb+( ray*cosd(i), ray*sind(i), 0 );
oneline := fieldlinepath( lenb, stp, -diffstep, vecfunc );
draw oneline withpen grossa;
% draw oneline withpen fina withcolor background;
endfor;
draw rp(posa) withpen grossa;
draw rp(posb) withpen grossa;
endfig;
Spread := 17;
f:= (10,-6,7);
beginfig(2);
numeric i, lena, lenb, numa, numb, sa, sb, diffstep, ang;
color stp;
path oneline;
pen grossa, fina;
grossa = pencircle scaled 3pt;
fina = pencircle scaled 2pt;
lena = 85;
lenb = 125;
numa = 0.03;
numb = 0.30;
diffstep = 0.2;
ang = -90;
sa = 1.5;
sb = 4.5;
for i=sa step numa until (1.5+sa):
stp := posa+i*cosd(ang)*green+i*sind(ang)*ncrossprod(perpd,green);
oneline := fieldlinepath( lena, stp, diffstep, potfunc );
draw oneline withpen grossa;
% draw oneline withpen fina withcolor background;
endfor;
ang := 180;
for i=sb step numb until (3.7+sb):
stp := posb+i*cosd(ang)*green+i*sind(ang)*ncrossprod(perpd,green);
oneline := fieldlinepath( lenb, stp, diffstep, potfunc );
draw oneline withpen grossa;
% draw oneline withpen fina withcolor background;
endfor;
draw rp(posa) withpen grossa;
draw rp(posb) withpen grossa;
endfig;
end.
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