其他人则描述了设计的一般框架(有限投影平面),并展示了如何生成素数阶的有限投影平面。我只想填补一些空白。
可以为许多不同的阶生成有限的投影平面,但是对于素数阶,它们最简单p
。然后,以整数为模p
的有限域可用于描述平面中点和线的坐标。有3种不同的点坐标:(1,x,y)
,(0,1,x)
,和(0,0,1)
,其中x
和y
可以采取的值从0
到p-1
。3种不同的点说明p^2+p+1
了系统中点数的公式。我们也可以形容线同为3种不同的坐标:[1,x,y]
,[0,1,x]
,和[0,0,1]
。
我们通过它们的坐标的点积是否等于0 mod来计算点和线是否入射p
。因此,例如,点(1,2,5)
和线[0,1,1]
从时p=7
起入射1*0+2*1+5*1 = 7 == 0 mod 7
,但点(1,3,3)
和线从时起[1,2,6]
不入射1*1+3*2+3*6 = 25 != 0 mod 7
。
翻译成卡片和图片的语言,这意味着具有坐标的卡片(1,2,5)
包含具有坐标的图片[0,1,1]
,但是具有坐标的卡片(1,3,3)
不包含具有坐标的图片[1,2,6]
。我们可以使用此过程来开发一张完整的卡片清单以及其中包含的图片。
顺便说一句,我认为将图片视为点,将卡视为线是容易的,但是点和线之间的投影几何结构存在双重性,所以这实际上没有关系。但是,接下来我将在图片中使用点,在卡片中使用线。
相同的构造适用于任何有限域。我们知道,q
当且仅当q=p^k
素数幂存在一个有限的阶域。该字段称为GF(p^k)
“加洛瓦字段”。在原始功率情况下,这些字段不像在原始情况下那样容易构造。
幸运的是,辛苦的工作已经在免费软件Sage中完成并实现了。例如,要获得第4阶的投影平面设计,只需键入
print designs.ProjectiveGeometryDesign(2,1,GF(4,'z'))
然后您将获得如下输出
ProjectiveGeometryDesign<points=[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13, 14, 15, 16, 17, 18, 19, 20], blocks=[[0, 1, 2, 3, 20], [0,
4, 8, 12, 16], [0, 5, 10, 15, 19], [0, 6, 11, 13, 17], [0, 7, 9, 14,
18], [1, 4, 11, 14, 19], [1, 5, 9, 13, 16], [1, 6, 8, 15, 18], [1, 7,
10, 12, 17], [2, 4, 9, 15, 17], [2, 5, 11, 12, 18], [2, 6, 10, 14, 16],
[2, 7, 8, 13, 19], [3, 4, 10, 13, 18], [3, 5, 8, 14, 17], [3, 6, 9, 12,
19], [3, 7, 11, 15, 16], [4, 5, 6, 7, 20], [8, 9, 10, 11, 20], [12, 13,
14, 15, 20], [16, 17, 18, 19, 20]]>
我对以上内容的解释如下:从0到20标记了21张图片。每个块(投影几何中的线)告诉我哪些图片出现在卡上。例如,第一张卡片的图片为0、1、2、3和20;第二张卡上将显示图片0、4、8、12和16;等等。
订单7的系统可以通过以下方式生成
print designs.ProjectiveGeometryDesign(2,1,GF(7))
产生输出
ProjectiveGeometryDesign<points=[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46,
47, 48, 49, 50, 51, 52, 53, 54, 55, 56], blocks=[[0, 1, 2, 3, 4, 5, 6,
56], [0, 7, 14, 21, 28, 35, 42, 49], [0, 8, 16, 24, 32, 40, 48, 50], [0,
9, 18, 27, 29, 38, 47, 51], [0, 10, 20, 23, 33, 36, 46, 52], [0, 11, 15,
26, 30, 41, 45, 53], [0, 12, 17, 22, 34, 39, 44, 54], [0, 13, 19, 25,
31, 37, 43, 55], [1, 7, 20, 26, 32, 38, 44, 55], [1, 8, 15, 22, 29, 36,
43, 49], [1, 9, 17, 25, 33, 41, 42, 50], [1, 10, 19, 21, 30, 39, 48,
51], [1, 11, 14, 24, 34, 37, 47, 52], [1, 12, 16, 27, 31, 35, 46, 53],
[1, 13, 18, 23, 28, 40, 45, 54], [2, 7, 19, 24, 29, 41, 46, 54], [2, 8,
14, 27, 33, 39, 45, 55], [2, 9, 16, 23, 30, 37, 44, 49], [2, 10, 18, 26,
34, 35, 43, 50], [2, 11, 20, 22, 31, 40, 42, 51], [2, 12, 15, 25, 28,
38, 48, 52], [2, 13, 17, 21, 32, 36, 47, 53], [3, 7, 18, 22, 33, 37, 48,
53], [3, 8, 20, 25, 30, 35, 47, 54], [3, 9, 15, 21, 34, 40, 46, 55], [3,
10, 17, 24, 31, 38, 45, 49], [3, 11, 19, 27, 28, 36, 44, 50], [3, 12,
14, 23, 32, 41, 43, 51], [3, 13, 16, 26, 29, 39, 42, 52], [4, 7, 17, 27,
30, 40, 43, 52], [4, 8, 19, 23, 34, 38, 42, 53], [4, 9, 14, 26, 31, 36,
48, 54], [4, 10, 16, 22, 28, 41, 47, 55], [4, 11, 18, 25, 32, 39, 46,
49], [4, 12, 20, 21, 29, 37, 45, 50], [4, 13, 15, 24, 33, 35, 44, 51],
[5, 7, 16, 25, 34, 36, 45, 51], [5, 8, 18, 21, 31, 41, 44, 52], [5, 9,
20, 24, 28, 39, 43, 53], [5, 10, 15, 27, 32, 37, 42, 54], [5, 11, 17,
23, 29, 35, 48, 55], [5, 12, 19, 26, 33, 40, 47, 49], [5, 13, 14, 22,
30, 38, 46, 50], [6, 7, 15, 23, 31, 39, 47, 50], [6, 8, 17, 26, 28, 37,
46, 51], [6, 9, 19, 22, 32, 35, 45, 52], [6, 10, 14, 25, 29, 40, 44,
53], [6, 11, 16, 21, 33, 38, 43, 54], [6, 12, 18, 24, 30, 36, 42, 55],
[6, 13, 20, 27, 34, 41, 48, 49], [7, 8, 9, 10, 11, 12, 13, 56], [14, 15,
16, 17, 18, 19, 20, 56], [21, 22, 23, 24, 25, 26, 27, 56], [28, 29, 30,
31, 32, 33, 34, 56], [35, 36, 37, 38, 39, 40, 41, 56], [42, 43, 44, 45,
46, 47, 48, 56], [49, 50, 51, 52, 53, 54, 55, 56]]>