arXiv subjects

Hasan Mahmood

Publications and source records attributed to Hasan Mahmood.

12 recordsLinked to original sources

arXiv2025

When are Morse resolutions polyhedral?

It is known that the chain complex of a simplex on $q$ vertices can be used to construct a free resolution of any ideal generated by $q$ monomials, and as a direct result, the Betti numbers always have binomial upper bounds, given by the number of faces of a simplex in each dimension. It is also known that for most monomials the resolution provided by the simplex is far from minimal. Discrete Morse theory provides an algorithm called \say{Morse matchings} by which faces of the simplex can be removed so that the chain complex on the remaining faces is still a free resolution of the same ideal. An immediate positive effect is an often considerable improvement on the bounds on Betti numbers. A caveat is the loss of the combinatorial structure of the simplex we started with: the output of the Morse matching process is a cell complex with no obvious structure besides an \say{address} for each cell. The main question in this paper is: which Morse matchings lead to Morse complexes that are polyhedral cell complexes? We prove that if a monomial ideal is minimally generated by up to four generators, then there is a maximal Morse matching of the simplex such that the resulting cell complex is a polyhedral cell complex. We then give an example of a monomial ideal minimally generated by six generators whose minimal free resolution is supported on a Morse complex and the Morse complex cannot be polyhedral no matter what Morse matching is chosen, and we go further to show that this ideal cannot have any polyhedral minimal free resolution.

math.AC↗

arXiv2025

Simplicial Resolutions of the Quadratic Power of Monomial Ideals

Given any monomial ideal $ I $ minimally generated by $ q $ monomials, we define a simplicial complex $\mathbb{M}_q^2$ that supports a resolution of $ I^2 $. We also define a subcomplex $\mathbb{M}^2(I)$, which depends on the monomial generators of $I$ and also supports the resolution of $ I^2 $. As a byproduct, we obtain bounds on the projective dimension of the second power of any monomial ideal. We also establish bounds on the Betti numbers of $ I^2 $, which are significantly tighter than those determined by the Taylor resolution of $ I^2 $. Moreover, we introduce the permutation ideal $\mathcal{T}_q$ which is generated by $q$ monomials. For any monomial ideal $I$ with $q$ generators, we establish that $\beta(I^2) \leq \beta({\mathcal{T}_q}^2)$. We show that the simplicial complex $\mathbb{M}_q^2$ supports the minimal resolution of ${\mathcal{T}_q}^2$. In fact, $\mathbb{M}_q^2$ is the Scarf complex of ${\mathcal{T}_q}^2$.

math.AC↗

arXiv2022

Operator Deformations and T-duality via Parallel Transport

We consider deformations of CFTs from the perspective of parallel transport in moduli space. In particular, we show how the deformations of individual operators can be computed and we also explore how these ideas can be extended to more general QFTs lacking conformal symmetry. We explore how to write one theory in terms of operators defined in a nearby theory, related to the first by a parallel transport in theory space. Using this construction, we describe how T-duality can be realised and how this provides a different perspective from the usual Buscher construction.

hep-th↗

arXiv2022

Interference Aware Cooperative Routing for Edge Computing-enabled 5G Networks

Recently, there has been growing research on developing interference-aware routing (IAR) protocols for supporting multiple concurrent transmission in next-generation wireless communication systems. The existing IAR protocols do not consider node cooperation while establishing the routes because motivating the nodes to cooperate and modeling that cooperation is not a trivial task. In addition, the information about the cooperative behavior of a node is not directly visible to neighboring nodes. Therefore, in this paper, we develop a new routing method in which the nodes' cooperation information is utilized to improve the performance of edge computing-enabled 5G networks. The proposed metric is a function of created and received interference in the network. The received interference term ensures that the Signal to Interference plus Noise Ratio (SINR) at the route remains above the threshold value, while the created interference term ensures that those nodes are selected to forward the packet that creates low interference for other nodes. The results show that the proposed solution improves ad hoc networks' performance compared to conventional routing protocols in terms of high network throughput and low outage probability.

eess.SP↗

arXiv2021

Torus Bundles, Automorphisms and T-Duality

We reconsider some older constructions of T-duality, based on automorphisms of the worldsheet operator algebra, in a modern context. It has been long known that at special points in the moduli space of torus compactifications, the target space gauge symmetry may be enhanced. Away from such points the symmetry is broken and T-duality may be understood as a residual discrete gauge symmetry that survives this breaking. Drawing on work on connections over the space of string backgrounds, we discuss how to generalise this framework for T-duality to geometric and non-geometric backgrounds that are not full solutions of string theory, but may play an important role in exact backgrounds. Along the way we find an interesting algebraic structure and discuss its relationship with doubled geometry. We comment on non-isometric T-duality in this context.

hep-th↗

arXiv2020

Classification of Planar Graphs Associated to the Ideal of the Numerical Semigroup

Let $Λ$ be a numerical semigroup and $I\subset Λ$ be an ideal of $Λ$. The graph $G_I(Λ)$ assigned to an ideal $I$ of $Λ$ is a graph with elements of $(Λ\setminus I)^*$ as vertices and any two vertices $x,y$ are adjacent if and only if $x+y \in I$. In this paper we give a complete characterization (up to isomorphism ) of the graph $G_I(Λ)$ to be planar, where $I$ is an irreducible ideal of $Λ$. This will finally characterize non planar graphs $G_I(Λ)$ corresponding to irreducible ideal $I$.

math.AC↗

arXiv2020

Density of $f$-ideals and $f$-ideals in mixed small degrees

A squarefree monomial ideal is called an $f$-ideal if its Stanley-Reisner and facet simplicial complexes have the same $f$-vector. We show that $f$-ideals generated in a fixed degree have asymptotic density zero when the number of variables goes to infinity. We also provide novel algorithms to construct $f$-ideals generated in small degrees.

math.AC↗

arXiv2020

Quasi f-Simplicial Complexes and Quasi f-Graphs

The notion of $f$-ideal is recent and has so far been studied in several papers. In \cite{qfi}, the idea of $f$-ideal is generalized to quasi $f$-ideals, which is much larger class than the class of $f$-ideals. In this paper, we introduce the concept of quasi $f$-simplicial complex and quasi $f$-graph. We give a characterization of quasi $f$-graphs on $n$ vertices. A complete solution of connectedness of quasi $f$-simplicial complexes is described. We have also shown a method of constructing Cohen-Macaulay quasi $f$-graphs.

math.CO↗

arXiv2020

Quasi f-Ideals

The notion off-ideals is recent and has been studied in the papers[1] [2], [5], [10], [11], [12], [13], [14] and [15]. In this paper, we have generalized the idea off-ideals to quasi f-ideals. This extended class of ideals is much bigger than the class of all f-ideals. Apart from giving various characterizations of quasi f-ideals of degree 2, we have determined all the minimal primes ideals of these ideals. Moreover, construction of quasi f-ideals of degree 2 has been described; the formula for computing Hilbert function and Hilbert series of the polynomial ring modulo quasi f-ideal has been provided.

math.AC↗

arXiv2020

The $\mathcal{N}\mathcal{F}$-Number of a Simplicial Complex

Let $Δ$ be a simplicial complex on $[n]$. The $\mathcal{N}\mathcal{F}$-complex of $Δ$ is the simplicial complex $δ_{\mathcal{N}\mathcal{F}}(Δ)$ on $[n]$ for which the facet ideal of $Δ$ is equal to the Stanley--Reisner ideal of $δ_{\mathcal{N}\mathcal{F}}(Δ)$. Furthermore, for each $k = 2,3,\ldots$\,, we introduce {\em $k^{th}$ $\mathcal{N}\mathcal{F}$-complex} $δ^{(k)}_{\mathcal{N}\mathcal{F}}(Δ)$ which is inductively defined by $δ^{(k)}_{\mathcal{N}\mathcal{F}}(Δ) = δ_{\mathcal{N}\mathcal{F}}(δ^{(k-1)}_{\mathcal{N}\mathcal{F}}(Δ))$ with setting $δ^{(1)}_{\mathcal{N}\mathcal{F}}(Δ) = δ_{\mathcal{N}\mathcal{F}}(Δ)$. One can set $δ^{(0)}_{\mathcal{N}\mathcal{F}}(Δ) = Δ$. The $\mathcal{N}\mathcal{F}$-number of $Δ$ is the smallest integer $k > 0$ for which $δ^{(k)}_{\mathcal{N}\mathcal{F}}(Δ) \simeq Δ$. In the present paper we are especially interested in the $\mathcal{N}\mathcal{F}$-number of a finite graph, which can be regraded as a simplicial complex of dimension one. It is shown that the $\mathcal{N}\mathcal{F}$-number of the finite graph $K_n\coprod K_m$ on $[n + m]$, which is the disjoint union of the complete graphs $K_n$ on $[n]$ and $K_m$ on $[m]$, where $n \geq 2$ and $m \geq 2$ with $(n,m) \neq (2,2)$, is equal to $n + m + 2$. Its corollary says that the $\mathcal{N}\mathcal{F}$-number of the complete bipartite graph $K_{n,m}$ on $[n+m]$ is also equal to $n + m + 2$.

math.AC↗

arXiv2018

Accelerating Viterbi Algorithm using Custom Instruction Approach

In recent years, the decoding algorithms in communication networks are becoming increasingly complex aiming to achieve high reliability in correctly decoding received messages. These decoding algorithms involve computationally complex operations requiring high performance computing hardware, which are generally expensive. A cost-effective solution is to enhance the Instruction Set Architecture (ISA) of the processors by creating new custom instructions for the computational parts of the decoding algorithms. In this paper, we propose to utilize the custom instruction approach to efficiently implement the widely used Viterbi decoding algorithm by adding the assembly language instructions to the ISA of DLX, PicoJava II and NIOS II processors, which represent RISC, stack and FPGA-based soft-core processor architectures, respectively. By using the custom instruction approach, the execution time of the Viterbi algorithm is significantly improved by approximately 3 times for DLX and PicoJava II, and by 2 times for NIOS II.

cs.AR↗

arXiv2015

Study of the effect of semi-infinite crystalline electrodes on transmission of gold atomic wires using DFT

First principle calculations of the conductance of gold wires containing 3-8 atoms each with 2.39 Å bond length were performed using density functional theory. Three different configuration of wire/electrodes were used. For zigzag wire with semi-infinite crystalline electrodes, even-odd oscillation is observed which is consistent with the previously reported results. A lower conductance was observed for the chain in semi-infinite crystalline electrodes compared to the chains suspended in wire-like electrode. The calculated transmission spectrum for the straight and zig-zag wires suspended between semi-infinite crystalline electrodes showed suppression of transmission channels due to electron scattering occurring at the electrode-wire interface.

physics.comp-ph↗