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Igor Minevich

Publications and source records attributed to Igor Minevich.

14 recordsLinked to original sources
arXiv2025

Lights Out Puzzle in p Colors: Evolution of Quiet Patterns

The Lights Out Puzzle represents a cellular automaton based on a grid of squares where clicking a square changes its state and the states of surrounding squares. A "quiet pattern" is a way to click such that in the end, no change is effected. We introduce a way to "evolve" quiet patterns in smaller grids into ones in $p$ times larger grids when the number of possible states of a square is a prime $p$. Using elliptic curves, we also find that an inverse "de-evolution" exists for most $p$. We also describe the only ways to click a grid of squares such that only 5 (the minimum) number of squares have a nonzero state.

nlin.CG↗
arXiv2025

Graph Powers of Groups II: The RA Matrix

For a graph $\Gamma$ and group $G$, $G^\Gamma$ is the subgroup of $G^{|\Gamma|}$ generated by elements with $g$ in the coordinates corresponding to $v$ and its neighbors in $\Gamma$. There is a natural epimorphism $G^\Gamma \to (G/[G,G])^\Gamma$ with kernel $[G,G]^n \cap G^\Gamma$. When $[G,G]^n \leq G^\Gamma$, the structure of $G^\Gamma$ is easily described from $(G/[G,G])^\Gamma$. Fixing $\Gamma$, if $[G,G]^{|\Gamma|} \leq G^\Gamma$ for all $G$, we say that $\Gamma$ is RA (reducible to abelian). We showed in [2] that wide classes of graphs are RA, including graphs of girth 5 or more. The key tool is the RA matrix $C_{\Gamma}$, and we showed that $\Gamma$ is RA if and only if the row space $Row(C_\Gamma) = \mathbb Z^{|\Gamma|}$. Here, we study the possibilities for the elementary divisors of $C_\Gamma$; the more nontrivial elementary divisors we get, the further $\Gamma$ is from being RA (and the harder $G^\Gamma$ is to describe). We show that while many graphs, including those of girth 4, cartesian products, and most tensor products have at most one nontrivial elementary divisor, one can construct a graph of girth 3 with any prescribed set of elementary divisors and $\mathbb Z$-nullity.

math.CO↗
arXiv2025

A quadrilateral half-turn theorem

If $ABC$ is a given triangle in the plane, $P$ is any point not on the extended sides of $ABC$ or its anticomplementary triangle, $Q$ is the complement of the isotomic conjugate of $P$ with respect to $ABC$, $DEF$ is the cevian triangle of $P$, and $D_0$ and $A_0$ are the midpoints of segments $BC$ and $EF$, respectively, a synthetic proof is given for the fact that the complete quadrilateral defined by the lines $AP, AQ, D_0Q, D_0A_0$ is perspective by a Euclidean half-turn to the similarly defined complete quadrilateral for the isotomic conjugate $P'$ of $P$ . This fact is used to define and prove the existence of a generalized circumcenter and generalized orthocenter for any such point $P$.

math.AG↗
arXiv2025

Graph Powers of Groups

The Lights Out Puzzle, played on a graph $\Gamma$, has been studied using linear algebra over $\mathbb{F}_2$ and more generally over $\mathbb{Z}/k\mathbb{Z}$. We generalize the setting by allowing the states of vertices to be the elements of a group $G$, where a \textit{click} in vertex $v$ multiplies the state of $v$ and its neighbors by an element $g \in G$ on the right. Starting with the identity element $e \in G$ for all vertices, the totality of all achievable state configurations forms a group $G^{\Gamma}$. This group generalizes parallel products of group actions and provides a rich structure for analysis. For many graphs, which we term ``RA'' (reducible to abelian), the problem reduces -- regardless of $G$ -- to a linear algebra question over $\mathbb{Z}$. We discuss a chain of five different subgroups consisting of commutators and introduce techniques for showing that families of graphs are RA using each. In particular, using Heisenberg groups, we establish that a graph is RA precisely when a certain lattice spans $\mathbb{Z}^{|\Gamma|}$. While most graphs appear to be RA, we show the odd-dimensional cube graphs $Q_{2n+1}$ and folded cube graphs $\square_d$, for $d$ odd or 2, are not.

math.GR↗
arXiv2024

Parks: A Doubly Infinite Family of NP-Complete Puzzles and Generalizations of A002464

The Parks Puzzle is a paper-and-pencil puzzle game that is classically played on a square grid with different colored regions (the parks). The player needs to place a certain number of "trees" in each row, column, and park such that none are adjacent, even diagonally. We define a doubly-infinite family of such puzzles, the $(c, r)$-tree Parks puzzles, where there need be $c$ trees per column and $r$ per row. We then prove that for each $c$ and $r$ the set of $(c, r)$-tree puzzles is NP-complete. For each $c$ and $r$, there is a sequence of possible board sizes $m \times n$, and the number of possible puzzle solutions for these board sizes is a doubly-infinite generalization of OEIS sequence A002464, which itself describes the case $c = r = 1$. This connects the Parks puzzle to chess-based puzzle problems, as the sequence describes the number of ways to place non-attacking kings on a chessboard so that there is exactly one in each column and row (i.e. to place non-attacking dragon kings in shogi). These findings add yet another puzzle to the set of chess puzzles and expands the list of known NP-complete problems described.

cs.CC↗
arXiv2017

Real elliptic curves and cevian geometry

We study the elliptic curve $E_a: (ax+1)y^2+(ax+1)(x-1)y+x^2-x=0$, which we call the geometric normal form of an elliptic curve. We show that any elliptic curve whose $j$-invariant is real is isomorphic to a curve $E_a$ in geometric normal form, and show that for $a \notin \{0, -1, -9\}$, the points on $E_a$, minus a set of $6$ points, can be characterized in terms of the cevian geometry of a triangle.

math.GM↗
arXiv2017

Vertex positions of the generalized orthocenter and a related elliptic curve

We study triangles $ABC$ and points $P$ for which the generalized orthocenter $H$ corresponding to $P$ coincides with a vertex $A,B$, or $C$. The set of all such points $P$ is a union of three ellipses minus $6$ points. In addition, if $T_P$ is the affine map taking $ABC$ to the cevian triangle $DEF$ of $P$ with respect to $ABC$, $P'$ is the isotomic conjugate of $P$, and $T_{P'}$ is the affine map taking $ABC$ to the cevian triangle of $P'$, then we study the locus of points $P$ for which the map $\textsf{M}_P=T_p \circ K^{-1} \circ T_{P'}$ is a translation. Here, $K$ is the complement map for $ABC$, and $\textsf{M}_P$ is an affine map taking the circumconic of $ABC$ for $P$ to the inconic of $ABC$ for $P$. The locus in question turns out to be an elliptic curve minus $6$ points, which can be synthetically constructed using the geometry of the triangle.

math.MG↗
arXiv2016

Synthetic foundations of cevian geometry, IV: the TCC-perspector theorem

In this paper we give a completely synthetic proof of the TCC-perspector theorem, that the isogonal conjugate $γ(H)$ of the generalized orthocenter $H$ (defined in Part III of this series of papers), with respect to a triangle $ABC$ and a point $P$, is the perspector of the tangential triangle of $ABC$ and the circumcevian triangle (both with respect to the circumcircle) of the isogonal conjugate $γ(Q)$, where $Q$ is the complement of the isotomic conjugate $P'$ of the point $P$.

math.MG↗
arXiv2016

A cevian locus and the geometric construction of a special elliptic curve

In a previous paper we defined the circumconic of a triangle $ABC$ with respect to a point $P$ as the conic $\tilde C=T_{P'}^{-1}(N_{P'})$, where $N_{P'}$ is the $9$-point conic for the quadrangle $ABCP'$ with respect to the line at infinity, $P'$ is the isotomic conjugate of $P$ with respect to $ABC$, and $T_{P'}$ is the affine map taking $ABC$ to the cevian triangle for $P'$. In this paper we determine the locus of points for which a certain affine map $\textsf{M}$ taking the circumconic $\tilde C$ to the inconic $\mathcal{I}$, defined to be the unique conic tangent to the sides of $ABC$ at the traces of the point $P$ on those sides, is a half-turn. This locus turns out to be an elliptic curve minus six points, which can be constructed geometrically using a family of affine maps defined for points on three open arcs of a circle.

math.HO↗
arXiv2015

Synthetic foundations of cevian geometry II: The center of the cevian conic

This paper continues the investigation of Part I, by studying the conic $\mathcal{C}_P$ on the five points $ABCPQ$, where $ABC$ is a given ordinary triangle and $Q$ is the isotomcomplement of $P$, defined as the complement of the isotomic conjugate $P'$ of $P$ with respect to triangle $ABC$. We show that $\mathcal{C}_P$ also lies on the points $P'$ and $Q'$, where $Q'$ is the isotomcomplement of $P'$. The conic $\mathcal{C}_P$ lies on six other points which are the images of the vertices of $ABC$ under the affine mapping $λ=T_{P'} \circ T_P^{-1}$ and its inverse, where $T_P$ and $T_{P'}$ are the unique affine maps taking $ABC$ to the cevian triangles of $P$ and $P'$, respectively. In the paper we characterize the center $Z$ of $\mathcal{C}_P$ as the unique fixed point of $λ$ in the extended plane, when $\mathcal{C}_P$ is a parabola or an ellipse, and the unique ordinary fixed point of $λ$, when $\mathcal{C}_P$ is a hyperbola. We also show that $Z=GV \cdot T_P(GV)$, where $G$ is the centroid of $ABC$ and $V=PQ \cdot P'Q'$. When $P$ is the Gergonne point of $ABC$, this gives a new characterization of the Feuerbach point $Z$. All of our arguments are purely synthetic.

math.MG↗
arXiv2015

Synthetic foundations of cevian geometry, III: The generalized orthocenter

In this paper, the third in the series, we define the generalized orthocenter $H$ corresponding to a point $P$, with respect to triangle $ABC$, as the unique point for which the lines $HA, HB, HC$ are parallel, respectively, to $QD, QE, QF$, where $DEF$ is the cevian triangle of $P$ and $Q=K \circ ι(P)$ is the $isotomcomplement$ of $P$, both with respect to $ABC$. We prove a generalized Feuerbach Theorem, and characterize the center $Z$ of the cevian conic $\mathcal{C}_P$, defined in Part II, as the center of the affine map $Φ_P = T_P \circ K^{-1} \circ T_{P'} \circ K^{-1}$, where $T_P$ is the unique affine map for which $T_P(ABC)=DEF$; $T_{P'}$ is defined similarly for the isotomic conjugate $P'=ι(P)$ of $P$; and $K$ is the complement map. The affine map $Φ_P$ fixes $Z$ and takes the nine-point conic $\mathcal{N}_H$ for the quadrangle $ABCH$ (with respect to the line at infinity) to the inconic $\mathcal{I}$, defined to be the unique conic which is tangent to the sides of $ABC$ at the points $D, E, F$. The point $Z$ is therefore the point where the nine-point conic $\mathcal{N}_H$ and the inconic $\mathcal{I}$ touch. This theorem generalizes the usual Feuerbach theorem and holds in all cases where the point $P$ is not on a median, whether the conics involved are ellipses, parabolas, or hyperbolas, and also holds when $Z$ is an infinite point. We also determine the locus of points $P$ for which the generalized orthocenter $H$ coincides with a vertex of $ABC$; this locus turns out to be the union of three conics minus six points. All our proofs are synthetic, and combine affine and projective arguments.

math.MG↗
arXiv2015

Synthetic foundations of cevian geometry, I: Fixed points of affine maps in triangle geometry

We give synthetic proofs of many new results in triangle geometry, focusing especially on fixed points of certain affine maps which are defined in terms of the cevian triangle $DEF$ of a point $P$ with respect to a given triangle $ABC$, as well as the cevian triangle of the isotomic conjugate $P'$ of $P$ with respect to $ABC$. We prove a formula for the cyclocevian map in terms of the isotomic and isogonal maps using an entirely synthetic argument, and show that the complement $Q$ of the isotomic conjugate $P'$ has many interesting properties. If $T_P$ is the affine map taking $ABC$ to $DEF$, we show synthetically that $Q$ is the unique ordinary fixed point of $T_P$ when $P$ is any point not lying on the sides of triangle $ABC$, its anti-complementary triangle, or the Steiner circumellipse of $ABC$. We also show that $T_P(Q')=P$ if $Q'$ is the complement of $P$, and that the affine map $T_P T_{P'}$ is either a homothety or a translation which always has the $P$-ceva conjugate of $Q$ as a fixed point. Finally, we show that $P$ lies on the Steiner circumellipse if and only if $T_PT_{P'}=K^{-1}$, where $K$ is the complement map for $ABC$. This paper forms the foundation for several more papers to follow, in which the conic on the 5 points $A,B,C,P,Q$ is studied and its center is characterized as a fixed point of the map $λ=T_{P'} T_P^{-1}$.

math.GM↗