arXiv subjects

Maksim Nikolaev

Publications and source records attributed to Maksim Nikolaev.

4 recordsLinked to original sources

arXiv2026

RISC-V Functional Safety for Autonomous Automotive Systems: An Analytical Framework and Research Roadmap for ML-Assisted Certification

RISC-V is emerging as a viable platform for automotive-grade embedded computing, with recent ISO 26262 ASIL-D certifications demonstrating readiness for safety-critical deployment in autonomous driving systems. However, functional safety in automotive systems is fundamentally a certification problem rather than a processor problem. The dominant costs arise from diagnostic coverage analysis, toolchain qualification, fault injection campaigns, safety-case generation, and compliance with ISO 26262, ISO 21448 (SOTIF), and ISO/SAE 21434. This paper analyzes the role of RISC-V in automotive functional safety, focusing on ISA openness, formal verifiability, custom extension control, debug transparency, and vendor-independent qualification. We examine autonomous driving safety requirements and map them to RISC-V architectural challenges such as lockstep execution, safety islands, mixed-criticality isolation, and secure debug. Rather than proposing a single algorithmic breakthrough, we present an analytical framework and research roadmap centered on certification economics as the primary optimization objective. We also discuss how selected ML methods, including LLM-assisted FMEDA generation, knowledge-graph-based safety case automation, reinforcement learning for fault injection, and graph neural networks for diagnostic coverage, can support certification workflows. We argue that the strongest outcome is not a faster core, but an ASIL-D-ready certifiable RISC-V platform.

cs.SE↗

arXiv2024

Greedy Conjecture for the Shortest Common Superstring Problem and its Strengthenings

In the Shortest Common Superstring problem, one needs to find the shortest superstring for a set of strings. This problem is APX-hard, and many approximation algorithms were proposed, with the current best approximation factor of 2.466. Whereas these algorithms are technically involved, for more than thirty years the Greedy Conjecture remains unsolved, that states that the Greedy Algorithm ``take two strings with the maximum overlap; merge them; repeat'' is a 2-approximation. This conjecture is still open, and one way to approach it is to consider its stronger version, which may make the proof easier due to the stronger premise or provide insights from its refutation. In this paper, we propose two directions to strengthen the conjecture. First, we introduce the Locally Greedy Algorithm (LGA), that selects a pair of strings not with the largest overlap but with the \emph{locally largest} overlap, that is, the largest among all pairs of strings with the same first or second string. Second, we change the quality metric: instead of length, we evaluate the solution by the number of occurrences of an arbitrary symbol. Despite the double strengthening, we prove that LGA is a \emph{uniform} 4-approximation, that is, it always constructs a superstring with no more than four times as many occurrences of an arbitrary symbol as any other superstring. At the same time, we discover the limitations of the greedy heuristic: we show that LGA is at least 3-approximation, and the Greedy Algorithm is at least uniform 2.5-approximation. These result show that if the Greedy Conjecture is true, it is not because the Greedy Algorithm is locally greedy or is uniformly 2-approximation.

cs.DS↗

arXiv2021

All instantiations of the greedy algorithm for the shortest superstring problem are equivalent

In the Shortest Common Superstring problem (SCS), one needs to find the shortest superstring for a set of strings. While SCS is NP-hard and MAX-SNP-hard, the Greedy Algorithm "choose two strings with the largest overlap; merge them; repeat" achieves a constant factor approximation that is known to be at most 3.5 and conjectured to be equal to 2. The Greedy Algorithm is not deterministic, so its instantiations with different tie-breaking rules may have different approximation factors. In this paper, we show that it is not the case: all factors are equal. To prove this, we show how to transform a set of strings so that all overlaps are different whereas their ratios stay roughly the same. We also reveal connections between the original version of SCS and the following one: find a~superstring minimizing the number of occurrences of a given symbol. It turns out that the latter problem is equivalent to the original one.

cs.DS↗

arXiv2020

Collapsing Superstring Conjecture

In the Shortest Common Superstring (SCS) problem, one is given a collection of strings, and needs to find a shortest string containing each of them as a substring. SCS admits $2\frac{11}{23}$-approximation in polynomial time (Mucha, SODA'13). While this algorithm and its analysis are technically involved, the 30 years old Greedy Conjecture claims that the trivial and efficient Greedy Algorithm gives a 2-approximation for SCS. We develop a graph-theoretic framework for studying approximation algorithms for SCS. The framework is reminiscent of the classical 2-approximation for Traveling Salesman: take two copies of an optimal solution, apply a trivial edge-collapsing procedure, and get an approximate solution. In this framework, we observe two surprising properties of SCS solutions, and we conjecture that they hold for all input instances. The first conjecture, that we call Collapsing Superstring conjecture, claims that there is an elementary way to transform any solution repeated twice into the same graph $G$. This conjecture would give an elementary 2-approximate algorithm for SCS. The second conjecture claims that not only the resulting graph $G$ is the same for all solutions, but that $G$ can be computed by an elementary greedy procedure called Greedy Hierarchical Algorithm. While the second conjecture clearly implies the first one, perhaps surprisingly we prove their equivalence. We support these equivalent conjectures by giving a proof for the special case where all input strings have length at most 3. We prove that the standard Greedy Conjecture implies Greedy Hierarchical Conjecture, while the latter is sufficient for an efficient greedy 2-approximate approximation of SCS. Except for its (conjectured) good approximation ratio, the Greedy Hierarchical Algorithm provably finds a 3.5-approximation.

cs.DS↗