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幾何学と代数系7章〜7.4節をGAViewerで触った際のメモ
default_model(p3ga),
a = red(e1), b = green(e2), c = blue(e3),

7.1 Homogeneous space

no + 0.1 e1 + 0.2 e2 + 0.3 e3,

10 no + e1 + 2 e2 + 3 e3,

7.2 Point at infinity

0.1 e1 + 0.2 e2 + 0.3 e3,

-0.1 e1 - 0.2 e2 - 0.3 e3,

7.3 Plucker coordinates of Line

7.3.1 expression of line

p1 = no + 0.1 e1 + 0.2 e2 + 0.3 e3,
p2 = no + 0.5 e1 + 0.5 e2 - 0.5 e3,

p1^p2,

m1 = 0.4,	m2 = 0.2,	m3 = -0.8,
n1 = -0.3,	n2 = 0.2,	n3 = - 0.1,
I= e1^e2^e3;

m1 e0^e1 + m2 e0^e2 + m3 e0^e3 + n1 e2^e3 + n2 e3^e1 + n3 e1^e2,

m = m1 e1 + m2 e2 + m3 e3,
n = n1 e1 + n2 e2 + n3 e3,
e0^m - ( - lcont(n, I)),

7.4 Plucker coordinates of Plane

clf(),
a = red(e1), b = green(e2), c = blue(e3),

7.4.1 expression of plane

p1 = no + 0.1 e1 + 0.2 e2 + 0.3 e3,
p2 = no + 0.5 e1 + 0.5 e2 - 0.5 e3,
p3 = no - 0.5 e1 - 0.2 e2 + 0.1 e3,
p1^p2^p3,
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