516 research outputs found
Representations of quivers and mixed graphs
This is a survey article for "Handbook of Linear Algebra", 2nd ed., Chapman &
Hall/CRC, 2014. An informal introduction to representations of quivers and
finite dimensional algebras from a linear algebraist's point of view is given.
The notion of quiver representations is extended to representations of mixed
graphs, which permits one to study systems of linear mappings and bilinear or
sesquilinear forms. The problem of classifying such systems is reduced to the
problem of classifying systems of linear mappings
A regularization algorithm for matrices of bilinear and sesquilinear forms
We give an algorithm that uses only unitary transformations and for each
square complex matrix constructs a *congruent matrix that is a direct sum of a
nonsingular matrix and singular Jordan blocks.Comment: 18 page
Canonical forms for complex matrix congruence and *congruence
Canonical forms for congruence and *congruence of square complex matrices
were given by Horn and Sergeichuk in [Linear Algebra Appl. 389 (2004) 347-353],
based on Sergeichuk's paper [Math. USSR, Izvestiya 31 (3) (1988) 481-501],
which employed the theory of representations of quivers with involution. We use
standard methods of matrix analysis to prove directly that these forms are
canonical. Our proof provides explicit algorithms to compute all the blocks and
parameters in the canonical forms. We use these forms to derive canonical pairs
for simultaneous congruence of pairs of complex symmetric and skew-symmetric
matrices as well as canonical forms for simultaneous *congruence of pairs of
complex Hermitian matrices.Comment: 31 page
Minkowski sums and Hadamard products of algebraic varieties
We study Minkowski sums and Hadamard products of algebraic varieties.
Specifically we explore when these are varieties and examine their properties
in terms of those of the original varieties.Comment: 25 pages, 7 figure
Normal matrices with a dominant eigenvalue and an eigenvector with no zero entries
AbstractWe say that a square complex matrix is dominant if it has an algebraically simple eigenvalue whose modulus is strictly greater than the modulus of any other eigenvalue; such an eigenvalue and any associated eigenvector are also said to be dominant. We explore inequalities that are sufficient to ensure that a normal matrix is dominant and has a dominant eigenvector with no zero entries. For a real symmetric matrix, these inequalities force the entries of a dominant real eigenvector to have a prescribed sign pattern. In the cases of equality in our inequalities, we find that exceptional extremal matrices must have a very special form
The Liquid Annular Reactor System (LARS) propulsion
A concept for very high specific impulse (greater than 2000 seconds) direct nuclear propulsion is described. The concept, termed the liquid annular reactor system (LARS), uses liquid nuclear fuel elements to heat hydrogen propellant to very high temperatures (approximately 6000 K). Operating pressure is moderate (approximately 10 atm), with the result that the outlet hydrogen is virtually 100 percent dissociated to monatomic H. The molten fuel is contained in a solid container of its own material, which is rotated to stabilize the liquid layer by centripetal force. LARS reactor designs are described, together with neutronic and thermal-hydraulic analyses. Power levels are on the order of 200 megawatts. Typically, LARS designs use seven rotating fuel elements, are beryllium moderated, and have critical radii of approximately 100 cm (core L/D approximately equal to 1.5)
Bounds on the spectral radius of a Hadamard product of nonnegative or positive semidefininte matrices
X. Zhan has conjectured that the spectral radius of the Hadamard product of two square nonnegative matrices is not greater than the spectral radius of their ordinary product. We prove Zhan’s conjecture, and a related inequality for positive semidefinite matrices, using standard facts about principal submatrices, Kronecker products, and the spectral radiu
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