803 research outputs found
Block-diagonal reduction of matrices over commutative rings I. (Decomposition of modules vs decomposition of their support)
Consider rectangular matrices over a commutative ring R. Assume the ideal of
maximal minors factorizes, I_m(A)=J_1*J_2. When is A left-right equivalent to a
block-diagonal matrix? (When does the module/sheaf Coker(A) decompose as the
corresponding direct sum?) If R is not a principal ideal ring (or a close
relative of a PIR) one needs additional assumptions on A. No necessary and
sufficient criterion for such block-diagonal reduction is known.
In this part we establish the following:
* The persistence of (in)decomposability under the change of rings. For
example, the passage to Noetherian/local/complete rings, the decomposability of
A over a graded ring R vs the decomposability of Coker(A) locally at the points
of Proj(R), the restriction to a subscheme in Spec(R).
* The necessary and sufficient condition for decomposability of square
matrices in the case: det(A)=f_1*f_2 is not a zero divisor and f_1,f_2 are
co-prime.
As an immediate application we give criteria of simultaneous (block-)diagonal
reduction for tuples of matrices over a field, i.e. linear determinantal
representations
Comparing Multidimensional Poverty between Egypt and Tunisia
It is common to argue that poverty is a multidimensional issue. Yet few studies have included the various dimensions of deprivation to yield a broader and fuller picture of poverty. The present paper considers the multidimensional aspects of deprivation by specifying a poverty line for each aspect and combines their associated one-dimensional poverty-gaps into multidimensional poverty measures. An application of these measures to compare poverty between Egypt and Tunisia is illustrated using robustness analysis and household data from each country.Multidimensional poverty indices, Robustness analysis, Egypt, Tunisia
On tree decomposability of Henneberg graphs
In this work we describe an algorithm that generates well constrained geometric constraint graphs which are solvable by the tree-decomposition constructive technique. The algorithm is based on Henneberg constructions and would be of help in transforming underconstrained problems into well constrained problems as well as in exploring alternative constructions over a given set of geometric elements.Postprint (published version
Higher-order interference and single-system postulates characterizing quantum theory
We present a new characterization of quantum theory in terms of simple
physical principles that is different from previous ones in two important
respects: first, it only refers to properties of single systems without any
assumptions on the composition of many systems; and second, it is closer to
experiment by having absence of higher-order interference as a postulate, which
is currently the subject of experimental investigation. We give three
postulates -- no higher-order interference, classical decomposability of
states, and strong symmetry -- and prove that the only non-classical
operational probabilistic theories satisfying them are real, complex, and
quaternionic quantum theory, together with 3-level octonionic quantum theory
and ball state spaces of arbitrary dimension. Then we show that adding
observability of energy as a fourth postulate yields complex quantum theory as
the unique solution, relating the emergence of the complex numbers to the
possibility of Hamiltonian dynamics. We also show that there may be interesting
non-quantum theories satisfying only the first two of our postulates, which
would allow for higher-order interference in experiments while still respecting
the contextuality analogue of the local orthogonality principle.Comment: 21 + 6 pages, 1 figure. v4: published version (includes several minor
corrections
Competing through business models
In this article a business model is defined as the firm choices on policies, assets and governance structure of those policies and assets, together with their consequences, be them flexible or rigid. We also provide a way to represent such business models to highlight the dynamic loops and to facilitate understanding interaction with other business models. Furthermore, we develop some tests to evaluate the goodness of a business model both in isolation as well as in interaction with other business models of different organizations, be those competitors, complements, suppliers, partners, etc.Business model; Interaction; Competitive Strategy; Competitive Dynamics;
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