1,172 research outputs found
Linear Projections of the Vandermonde Polynomial
An n-variate Vandermonde polynomial is the determinant of the n x n matrix
where the ith column is the vector (1, x_i, x_i^2, ...., x_i^{n-1})^T.
Vandermonde polynomials play a crucial role in the theory of alternating
polynomials and occur in Lagrangian polynomial interpolation as well as in the
theory of error correcting codes. In this work we study structural and
computational aspects of linear projections of Vandermonde polynomials.
Firstly, we consider the problem of testing if a given polynomial is linearly
equivalent to the Vandermonde polynomial. We obtain a deterministic polynomial
time algorithm to test if the polynomial f is linearly equivalent to the
Vandermonde polynomial when f is given as product of linear factors. In the
case when the polynomial f is given as a black-box our algorithm runs in
randomized polynomial time. Exploring the structure of projections of
Vandermonde polynomials further, we describe the group of symmetries of a
Vandermonde polynomial and show that the associated Lie algebra is simple.Comment: Submitted to a conferenc
Lower bounds for multilinear bounded order ABPs
Proving super-polynomial size lower bounds for syntactic multilinear
Algebraic Branching Programs(smABPs) computing an explicit polynomial is a
challenging problem in Algebraic Complexity Theory. The order in which
variables in appear along source to sink paths in any
smABP can be viewed as a permutation in . In this article, we consider the
following special classes of smABPs where the order of occurrence of variables
along a source to sink path is restricted:
Strict circular-interval ABPs: For every subprogram the index set of
variables occurring in it is contained in some circular interval of
.
L-ordered ABPs: There is a set of L permutations of variables such that every
source to sink path in the ABP reads variables in one of the L orders.
We prove exponential lower bound for the size of a strict circular-interval
ABP computing an explicit n-variate multilinear polynomial in VP. For the same
polynomial, we show that any sum of L-ordered ABPs of small size will require
exponential () many summands, when . At the heart of above lower bound arguments
is a new decomposition theorem for smABPs: We show that any polynomial
computable by an smABP of size S can be written as a sum of O(S) many
multilinear polynomials where each summand is a product of two polynomials in
at most 2n/3 variables computable by smABPs. As a corollary, we obtain a low
bottom fan-in version of the depth reduction by Tavenas [MFCS 2013] in the case
of smABPs. In particular, we show that a polynomial having size S smABPs can be
expressed as a sum of products of multilinear polynomials on
variables, where the total number of summands is bounded by . Additionally, we show that L-ordered ABPs can be transformed into
L-pass smABPs with a polynomial blowup in size
New Algorithms and Hard Instances for Non-Commutative Computation
Motivated by the recent developments on the complexity of
non-com\-mu\-ta\-tive determinant and permanent [Chien et al.\ STOC 2011,
Bl\"aser ICALP 2013, Gentry CCC 2014] we attempt at obtaining a tight
characterization of hard instances of non-commutative permanent.
We show that computing Cayley permanent and determinant on weight\-ed
adjacency matrices of graphs of component size six is complete on
algebras that contain matrices and the permutation group .
Also, we prove a lower bound of on the size of branching
programs computing the Cayley permanent on adjacency matrices of graphs with
component size bounded by two. Further, we observe that the lower bound holds
for almost all graphs of component size two.
On the positive side, we show that the Cayley permanent on graphs of
component size can be computed in time , where is a
parameter depending on the labels of the vertices.
Finally, we exhibit polynomials that are equivalent to the Cayley permanent
polynomial but are easy to compute over commutative domains.Comment: Submitted to a conferenc
Parameterized Analogues of Probabilistic Computation
We study structural aspects of randomized parameterized computation. We
introduce a new class - as a natural parameterized
analogue of . Our definition uses the machine based characterization
of the parameterized complexity class obtained by Chen et.al [TCS
2005]. We translate most of the structural properties and characterizations of
the class to the new class -.
We study a parameterization of the polynomial identity testing problem based
on the degree of the polynomial computed by the arithmetic circuit. We obtain a
parameterized analogue of the well known Schwartz-Zippel lemma [Schwartz, JACM
80 and Zippel, EUROSAM 79].
Additionally, we introduce a parameterized variant of permanent, and prove
its completeness.Comment: Submitted to a conferenc
Limitations of sum of products of Read-Once Polynomials
We study limitations of polynomials computed by depth two circuits built over
read-once polynomials (ROPs) and depth three syntactically multi-linear
formulas.
We prove an exponential lower bound for the size of the
arithmetic circuits built over syntactically
multi-linear arithmetic circuits computing a
product of variable disjoint linear forms on variables. We extend the
result to the case of arithmetic circuits built over
ROPs of unbounded depth, where the number of variables with gates as a
parent in an proper sub formula is bounded by . We show that the
same lower bound holds for the permanent polynomial. Finally we obtain an
exponential lower bound for the sum of ROPs computing a polynomial in defined by Raz and Yehudayoff.
Our results demonstrate a class of formulas of unbounded depth with
exponential size lower bound against the permanent and can be seen as an
exponential improvement over the multilinear formula size lower bounds given by
Raz for a sub-class of multi-linear and non-multi-linear formulas.
Our proof techniques are built on the one developed by Raz and later extended
by Kumar et. al.\cite{KMS13} and are based on non-trivial analysis of ROPs
under random partitions. Further, our results exhibit strengths and limitations
of the lower bound techniques introduced by Raz\cite{Raz04a}.Comment: Submitted to a conferenc
Regularity of Binomial Edge Ideals of Certain Block Graphs
We obtain an improved lower bound for the regularity of the binomial edge
ideals of trees. We prove an upper bound for the regularity of the binomial
edge ideals of certain subclass of block-graphs. As a consequence we obtain
sharp upper and lower bounds for the regularity of binomial edge ideals of a
class of trees called lobsters. We also obtain precise expressions for the
regularities of binomial edge ideals of certain classes of trees and block
graphs.Comment: Some more minor changes don
An upper bound for the regularity of binomial edge ideals of trees
In this article we obtain an improved upper bound for the regularity of
binomial edge ideals of trees.Comment: 6 pages. Journal of Algebra and its Applications (Accepted
Study of spin-phonon coupling and magnetic field induced spin reorientation in polycrystalline multiferroic
The present work reports the preparation of polycrystalline multiferroic
(GdFO) and characterization with x-ray diffraction (XRD),
magnetization, temperature dependent Raman spectroscopy, temperature and
magnetic field dependent Mssbauer spectroscopy
measurements. The sample is found to be phase pure from Rietveld refinement of
XRD pattern. The Mssbauer spectra measured in the presence of
external magnetic field show the signatures of field induced spin reorientation
transition, which are corroborated by magnetization measurements. From the
temperature dependent variation of internal hyperfine field, Nel
transition temperature () of 672.50.2 K and critical exponent
() of 0.3330.003 is obtained. Temperature dependent (300 - 760 K)
Raman spectroscopy measurements show the signatures of spin-phonon coupling and
local structural re-arrangement across .Comment: 8 pages, 12 figure
On the Complexity of Matroid Isomorphism Problem
We study the complexity of testing if two given matroids are isomorphic. The
problem is easily seen to be in . In the case of linear matroids,
which are represented over polynomially growing fields, we note that the
problem is unlikely to be -complete and is \co\NP-hard. We show
that when the rank of the matroid is bounded by a constant, linear matroid
isomorphism, and matroid isomorphism are both polynomial time many-one
equivalent to graph isomorphism. We give a polynomial time Turing reduction
from graphic matroid isomorphism problem to the graph isomorphism problem.
Using this, we are able to show that graphic matroid isomorphism testing for
planar graphs can be done in deterministic polynomial time. We then give a
polynomial time many-one reduction from bounded rank matroid isomorphism
problem to graphic matroid isomorphism, thus showing that all the above
problems are polynomial time equivalent. Further, for linear and graphic
matroids, we prove that the automorphism problem is polynomial time equivalent
to the corresponding isomorphism problems. In addition, we give a polynomial
time membership test algorithm for the automorphism group of a graphic matroid
Magnetic and Hyperfine interactions in HoFe1-xCrxO3 compounds
We report on the magnetic and Mossbauer properties of polycrystalline
HoFe1-xCrxO3 compounds. Magnetization data reveals the continuous tailoring of
magnetic transition due to weakening of Ho3+ Fe3+ and Fe3+ Fe3+ interactions in
the entire temperature range by replacing the Fe3+ ions with Cr3+ ions. The
observed decrease in Neel temperature (TN) and increase in spin re-orientation
transition temperature (TSR) with the replacement of Fe3+ with Cr3+ is ascribed
to the weakening of Fe(Cr) O Fe(Cr) antiferromagnetic exchange interaction. In
addition, we also attribute such a change in TN to the enhancement of
ferromagnetic interaction of adjacent Cr3+ moments through t e hybridization as
a result of the structural distortion. The decrease in isomer shift (IS)
suggests enhancement of the interaction between nuclear charge with the 3s
electrons as a result of decrease in radial part of 3d wave function with Cr
addition. In this paper we also discuss about the variation of quadrupole
splitting (QS) and hyperfine fields (Hhf) with Cr addition in HoFe1-xCrxO3
compounds
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