摘要
本文研究有理方体与堆垒数论中的一些问题。得到的主要结果如下:
1.棱长和面对角线长均为有理数的长方体称为有理方体。找有理方体等价于解丢番图方程组:x~2+y~2=l~2,x~2+z~2=m~2,y~2+z~2=n~2。许多数学家(包括欧拉)都曾研究过这一问题,给出了许多参数解。对任一本原商高组(a,b,c),是否存在整数s,t使得s~2+t~2a~2,s~2+t~2b~2均为平方数呢?本文提出这一问题,并给出处理这个问题一般方法。一定意义上说,我们将这一问题归结为有限计算。
2.设A是k个正整数构成的集合。称{∑_(b∈B)b:B(?)A,B≠φ}为A的子集和集合,记为S(A).M.B.Nathanson在Trans.Am.Math.Soc.(1995,347(4):1409-1418)中研究了子集和的逆问题,并提出一个未解决问题。本文研究这一问题,提出如下猜想:若|A|=k≥ 6,gcd(A)=1,A中最大数为M,则同时给出这个猜想的部分证明。所得定理改进了Nathanson的结果。
3.设G为有限阿贝耳群。对满足条件|A|+|B|=|G|的G的非空子集A和B,我们确定了和集A+B={a+b:a∈A,b∈B}基数的所有可能取值,并描述使A+B≠G的那些子集A,B的结构。记
A(?)B={a+b:a∈A,b∈B,a≠b},L(G)=|{g:g∈G,2g=0}|。对满足|A|+|B|=|G|+L(G)的G的非空子集A和B,我们证明了|A(?)B|≥|G|-2,并完全描述使A(?)B≠G的那些子集A,B的结构。所得结果推广了L.Gallardo等人在Z/nZ中关于A(?)A的相应结论(J.London Math.Soc.2002,65(2):513-523)。
4.设A,B为整数区间[1,n]的两个非空子集,t为正整数。定义
(A+B)_t={x∈A+B:至少存在t对(a,6)∈A×B使得x=a+b}。本文证明了:若|A|+|B|≥(4n+4t-3)/3,则(A+B)_t中包含一个长至少为|A|+|B|-2t+1连续整数块。利用我们的方法,我们还证明了:若|A|+|B|≥4n/3,则A+B中包含长为n的算术级数;对任一满足2≤r≤(4n-1)/3的整数r,存在[1,n]的两个非空子集A,B使得|A|+|B|=r,而A+B中算术级数长度至多为(r+2)/2,进而至多为(2n-1)/3+1。同时,我们给出了这些结果在A(?)B中的平行结论。
In this dissertation, we investigate rational cuboids and some problems in additive number theory. The main results are summarized as follows.
1. A rational cuboid is a rectangular parallelepiped whose edges and face diagonals all have rational lengths. The problem of finding rational cuboids has attracted much historical interest. Are there rational cuboids with a given face? We pose this problem and develop a general theory to deal with this problem. In a sense, we reduce this problem to a finite calculation.
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