Existence of magic 3‐dimensional rectangles

Since the complete solution for the existence of magic 2‐dimensional rectangles in 1881, much attention has been paid on the existence of magic l‐dimensional rectangles for . The existence problem for magic l‐dimensional rectangles with even sizes has been solved completely for all integers . However, very little is known for the existence of magic l‐dimensional rectangles () with odd sizes except for some families and a few sporadic examples. In this paper, we focus our attention on the existence of magic 3‐dimensional rectangles and prove that the necessary conditions for the existence of magic 3‐dimensional rectangles are also sufficient. Our construction method is mainly based on a new concept, symmetric zero‐sum subset partition, which plays a crucial role in the recursive constructions of magic 3‐rectangles similar to that of PBD in the PBD‐closure construction in combinatorial design theory.     

On nonsingular regular magic squares of odd order

Using centroskew matrices, we provide a necessary and sufficient condition for a regular magic square to be nonsingular. Using latin squares and circulant matrices we describe a method of construction of nonsingular regular magic squares of order n where n is an odd prime power.     

三阶乘积幻方的构造

通过构造幻方积最小的三阶乘积幻方给出了三阶乘积幻方可构造的一个充分必要条件,并完全确定了所有元素为不同正整数的三阶乘积幻方的结构.     

Existence of centre-complementary magic rectangles

A magic rectangle of size $(m_1,m_2)$ is an $m_1\times m_2$ array consisting of $m_1{m}_2$ consecutive integers in which the sum of each row is a constant and the sum of each column is another (different if $m_1\ne m_2$). It is centre-complementary if the sum of any pair of centrally symmetric positions is constant. As a natural generalization of symmetric magic squares, centre-complementary magic rectangles are instrumental in the construction of 3-dimensional rectangles. In this paper, we focus our attention on the existence of centre-complementary magic rectangles and prove that the necessary conditions for the existence of centre-complementary magic rectangles are also sufficient.     

Magic square spectra

To study the eigenvalues of low order singular and non-singular magic squares we begin with some aspects of general square matrices. Additional properties follow for general semimagic squares (same row and column sums), with further properties for general magic squares (semimagic with same diagonal sums). Parameterizations of general magic squares for low orders are examined, including factorization of the linesum eigenvalue from the characteristic polynomial.For nth order natural magic squares with matrix elements 1,…,n² we find examples of some remarkably singular cases. All cases of the regular (or associative, or symmetric) type (antipodal pair sum of 1+n²) with n-1 zero eigenvalues have been found in the only complete sets of these squares (in fourth and fifth order). Both the Jordan form and singular value decomposition (SVD) have been useful in this study which examines examples up to 8th order.In fourth order these give examples illustrating a theorem by Mattingly that even order regular magic squares have a zero eigenvalue with odd algebraic multiplicity, m. We find 8 cases with m=3 which have a non-diagonal Jordan form. The regular group of 48 squares is completed by 40 squares with m=1, which are diagonable. A surprise finding is that the eigenvalues of 16 fourth order pandiagonal magic squares alternate between m=1, diagonable, and m=3, non-diagonable, on rotation by π/2. Two 8th order natural magic squares, one regular and the other pandiagonal, are also examined, found to have m=5, and to be diagonable.Mattingly also proved that odd order regular magic squares have a zero eigenvalue with even multiplicity, m=0,2,4,... Analyzing results for natural fifth order magic squares from exact backtracking calculations we find 652 with m=2, and four with m=4. There are also 20, 604 singular seventh order natural ultramagic (simultaneously regular and pandiagonal) squares with m=2, demonstrating that the co-existence of regularity and pandiagonality permits singularity. The singular odd order examples studied are all non-diagonable.     

非素数阶幻方的构造

基于矩阵运算,给出任意双偶数阶和非素数阶幻方的新构造方法:1)由任一低阶m(m为偶数且m≠2)幻方生成一高阶2m阶幻方;2)利用已知的m(m≠2)阶和n(n≠2)阶两个幻方,构造任意的非素数mn阶幻方,加强一些条件后,进一步提出构造两类高级幻方(泛对角线幻方和关联幻方)的新方法.     

奇数阶泛对角线雪花幻方的构作

The constructional methods of pandiagonal snowflake magic squares of orders 4m are established in paper [3]. In this paper, the constructional methods of pandiagonal snowflake magic squares of odd orders n are established with n = 6m l, 6m 5 and 6m 3, m is an odd positive integer and m is an even positive integer 9|6m 3. It is seen that the number sets for constructing pandiagonal snowflake magic squares can be extended to the matrices with symmetric partial difference in each direction for orders 6m 1 , 6m 5; to the trisection matrices with symmetric partial difference in each direction for order 6m 3.     

求解奇数阶幻方的一个简单方法

运用等差数列的相关原理,给出一种构造奇数阶对称幻方的新方法——等差数列法.此方法简单、快捷、便于计算机操作,具有优越性.     

用线性取余变换造正交拉丁方和幻方

本文利用线性取余变换造正交拉丁方、幻方和泛对角线幻方。文［１］造奇数阶正交拉丁方的方法，文［２］的方法都本文方法的特例。     

A family of pandiagonal bimagic squares based on orthogonal arrays

In this article we give a construction of pandiagonal bimagic squares by means of four‐dimensional bimagic rectangles, which can be obtained from orthogonal arrays with special properties. In particular, we show that there exists a normal pandiagonal bimagic square of order n⁴ for all positive integer n≥7 such that gcd(n, 30) = 1 , which gives an answer to problem 22 of Abe in [Discrete Math 127 (1994), 3–13]. © 2011 Wiley Periodicals, Inc. J Combin Designs 19:427‐438, 2011     

用正交对角拉丁方及幻矩与和阵构作mn阶标准二次幻方

当m和n为同奇或同偶的正整数且m,n≠1,2,3,6时,用m和n阶正交对角拉丁方及{0,1,…,mn-1）上的m×n幻矩与和阵,构作了mn阶标准二次幻方．     

The Moore–Penrose inverse of block magic rectangles

As is known, a semi-magic square is an n?×?n matrix having the sum of entries in each row and each column equal to a constant. This note generalizes this notion and introduce a special class of block matrices called block magic rectangles. It is proved that the Moore–Penrose inverse of a block magic rectangle is also a block magic rectangle.     

The performance of Bank-Weiser's error estimator for quadrilateral finite elements

The error estimator proposed by Bank and Weiser is analyzed in the case of degree p finite element approximations on quadrilateral meshes. It is shown that the scheme is asymptotically exact in the energy norm for regular solutions provided that the degree of approximation is of odd order and the elements are rectangles. Perhaps surprisingly, the hypotheses are necessary, as counterexamples show. © 1994 John Wiley & Sons, Inc.     

On properties of special magic square matrices

By treating regular (or associative), pandiagonal, and most-perfect (MP) magic squares as matrices, we find a number of interesting properties and relationships. In addition, we introduce a new class of quasi-regular (QR) magic squares which includes regular and MP magic squares. These four classes of magic squares are called “special”.We prove that QR magic squares have signed pairs of eigenvalues just as do regular magic squares according to a well-known theorem of Mattingly. This leads to the fact that odd powers of QR magic squares are magic squares which also can be established directly from the QR condition. Since all pandiagonal magic squares of order 4 are MP, they are QR. Also, we show that all pandiagonal magic squares of order 5 are QR but higher-order ones may or may not be. In addition, we prove that odd powers of MP magic squares are MP. A simple proof is given of the known result that natural (or classic) pandiagonal and regular magic squares of singly-even order do not exist.We consider the reflection of a regular magic square about its horizontal or vertical centerline and prove that signed pairs of eigenvalues of the reflected square differ from those of the original square by the factor i. A similar result is found for MP magic squares and a subclass of QR magic squares.The paper begins with mathematical definitions of the special magic squares. Then, a number of useful matrix transformations between them are presented. Next, following a brief summary of the spectral analysis of matrices, the spectra of these special magic squares are considered and the results mentioned above are established. A few numerical examples are presented to illustrate our results.     

Solution of the wave equation in Rn + 1 with data on a characteristic cone

A unified treatment of the problem is presented for both odd and even space dimensions. In contrast to previous results for odd n, when the space dimension is even, there is no general existence although the uniqueness holds. A necessary and sufficient condition for admissible data is given. Of independent interest are several versions of the “Plancherel theorem” of the Radon transform, in the space L₂¹(Rⁿ) of all functions whose gradients are square integrable.     

Regular<Emphasis Type="Italic">n</Emphasis>-simplices in ℝ<Superscript><Emphasis Type="Italic">n</Emphasis></Superscript> with vertices in ℤ<Superscript><Emphasis Type="Italic">n</Emphasis></Superscript>

In this paper theI andII regularn-simplices are introduced. We prove that the sufficient and necessary conditions for existence of anI regularn-simplex in ℝ ⁿ are that ifn is even thenn = 4m(m + 1), and ifn is odd thenn = 4m + 1 with thatn + 1 can be expressed as a sum of two integral squares orn = 4m - 1, and that the sufficient and necessary condition for existence of aII regularn-simplex in ℝ ⁿ isn = 2m ² - 1 orn = 4m(m + 1)(m ∈ ℕ). The connection between regularn-simplex in ℝ ⁿ and combinational design is given.     

On Two Dimensional Packing

The paper considerspacking of rectanglesinto an infinite bin. Similar to theTetris game, the rectangles arrive from the top and, once placed, cannot be moved again. The rectangles are moved inside the bin to reach their place. For the case in which rotations are allowed, we design an algorithm whose performance ratio is constant. In contrast, if rotations are not allowed, we show that no algorithm of constant ratio exists. For this case we design an algorithm with performance ratio ofO(log(1/)), where is the minimum width of any rectangle. We also show that no algorithm can achieve a better ratio than for this case.     

Optimal rectangle packing

We consider the NP-complete problem of finding an enclosing rectangle of minimum area that will contain a given a set of rectangles. We present two different constraint-satisfaction formulations of this problem. The first searches a space of absolute placements of rectangles in the enclosing rectangle, while the other searches a space of relative placements between pairs of rectangles. Both approaches dramatically outperform previous approaches to optimal rectangle packing. For problems where the rectangle dimensions have low precision, such as small integers, absolute placement is generally more efficient, whereas for rectangles with high-precision dimensions, relative placement will be more effective. In two sets of experiments, we find both the smallest rectangles and squares that can contain the set of squares of size 1×1, 2×2,…,N×N, for N up to 27. In addition, we solve an open problem dating to 1966, concerning packing the set of consecutive squares up to 24×24 in a square of size 70×70. Finally, we find the smallest enclosing rectangles that can contain a set of unoriented rectangles of size 1×2, 2×3, 3×4,…,N×(N+1), for N up to 25.     

Regular path decompositions of odd regular graphs

Kotzig asked in 1979 what are necessary and sufficient conditions for a d‐regular simple graph to admit a decomposition into paths of length d for odd d>3. For cubic graphs, the existence of a 1‐factor is both necessary and sufficient. Even more, each 1‐factor is extendable to a decomposition of the graph into paths of length 3 where the middle edges of the paths coincide with the 1‐factor. We conjecture that existence of a 1‐factor is indeed a sufficient condition for Kotzig's problem. For general odd regular graphs, most 1‐factors appear to be extendable and we show that for the family of simple 5‐regular graphs with no cycles of length 4, all 1‐factors are extendable. However, for d>3 we found infinite families of d‐regular simple graphs with non‐extendable 1‐factors. Few authors have studied the decompositions of general regular graphs. We present examples and open problems; in particular, we conjecture that in planar 5‐regular graphs all 1‐factors are extendable. © 2009 Wiley Periodicals, Inc. J Graph Theory 63: 114–128, 2010