# Combinatorics and Graph Theory

## 1511 Submissions

[2] **viXra:1511.0225 [pdf]**
*replaced on 2015-12-05 16:57:21*

### Counting 2-way Monotonic Terrace Forms over Rectangular Landscapes

**Authors:** Richard J. Mathar

**Comments:** 27 Pages. Added Section 6 (cut sets) and removed the inconclusive Appendix B.

A terrace form assigns an integer altitude to each point of a finite two-dimensional square grid
such that the maximum altitude difference between a point and its four neighbors is one.
It is 2-way monotonic if the sign of this altitude difference is zero or one for steps to the East or steps
to the South. We provide tables for the number of 2-way monotonic terrace forms as a function of grid size
and maximum altitude difference, and point at the equivalence to the number of 3-colorings of the grid.

**Category:** Combinatorics and Graph Theory

[1] **viXra:1511.0015 [pdf]**
*submitted on 2015-11-02 15:32:57*

### A Class of Multinomial Permutations Avoiding Object Clusters

**Authors:** Richard J. Mathar

**Comments:** Pages 9 to 21 are a JAVA program distributed under the LGPL v3.

The multinomial coefficients count the number of ways (of permutations) of
placing a number of partially distinguishable objects on a line, taking ordering
into account. A well-known two-parametric family of counts arises if there are objects
of c distinguishable colors and m objects of each color, m*c objects in total, to be placed on line.
In this work we propose an algorithm to count the permutations where
no two objects of the same color appear side-by-side on the line. This eliminates
all permutations with "clusters" of colors. Essentially we represent filling
the line sequentially with objects as a tree of states where each node
matches one partially filled line. Subtrees are merged if they have the same
branching structure, and weights are assigned to nodes in the tree keeping track
of how many mergers take place. This is implemented in a JAVA program; numerical results
confirm Hardin's earlier counts for this kind of restricted permutations.

**Category:** Combinatorics and Graph Theory