Note on group postulates

Note on Group Postulates

A Note on Group Matrices1

If numerical values are given to the x then we call the resulting matrix "a" group matrix. This note gives a new characterization of hamiltonian groups by means of group matrices. A matrix A of complex numbers is called normal if AA*=A*A where A* is the transposed, complex conjugate of A. If the matrix also contains indeterminates we introduce formally their conjugates and define normality as b...

On Generalizing the AGM Postulates

The AGM theory is the dominating paradigm in the field of belief change but makes some non-elementary assumptions which disallow its application to certain logics. In this paper, we recast the theory by dropping most such assumptions; we determine necessary and sufficient conditions for a logic to support operators which are compatible with our generalized version of the theory and show that ou...

A note on the order graph of a group

 The order graph of a group $G$, denoted by $Gamma^*(G)$, is a graph whose vertices are subgroups of $G$ and two distinct vertices $H$ and $K$ are adjacent if and only if $|H|big{|}|K|$ or $|K|big{|}|H|$. In this paper, we study the connectivity and diameter of this  graph. Also we give a relation between the order graph and prime  graph of a group.

Note on Group Velocity and Energy Propagation

A general proof is given for the equality between group velocity and energy velocity for linear wave propagation in a homogeneous medium with arbitrary spatial and temporal dispersion. In the series of physics “Questions” in the American Journal of Physics, K. M. Awati and T. Howes ask for a general proof of the fact that in linear dispersive wave propagation, energy propagates at the group vel...