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Hristo Papazov

dblp:306/9902 · DBLP profile ↗
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3ranked-venue papers
2as first author
3since 2021 · last 2026
—ORCID · none

Domains — the database's venue-derived domains; a paper can count in several

Artificial intelligence and machine learning · 3 · 2 first-author · 3 since 2021

Expertise — from the expertise taxonomy: the topics of the expert's papers under the CCF categories. A weight counts papers with recency: 1 for a paper about the topic, 0.3 when the topic is its context, halved every five years.

Theoretical computer science
2 papers
Computational complexity · 52% Automata and formal languages · 48%
Artificial intelligence
1 paper
Learning theory · 100%

Topics — the 6 heaviest of 6, each with the papers that count most for it

TopicWeightPapersLastEvidence papers
Computational complexity
communication complexity
1.012026
Space-Efficient Language Generation in the Limit · COLT 2026
Automata and formal languages › language learning
language generation in the limit
1.012026
Space-Efficient Language Generation in the Limit · COLT 2026
Computational complexity › space complexity
space lower bounds
1.012026
Space-Efficient Language Generation in the Limit · COLT 2026
Machine learning › Learning theory
inductive inference
0.912025
Learning Algorithms in the Limit · COLT 2025
Machine learning › Learning theory › inductive inference
learning in the limit
0.912025
Learning Algorithms in the Limit · COLT 2025
Automata and formal languages › transducers
finite-state transducers
0.912025
Learning Algorithms in the Limit · COLT 2025

Methods — techniques the papers use, named apart from their topics

gold's inductive inference framework · 1.7computational observations · 1.7streaming algorithms · 1.0reduction · 1.0
YearPublicationVenuePosition
2026 Space-Efficient Language Generation in the Limit
abstract
We initiate a resource-aware theory of \textit{language generation in the limit} under the minimal constraint of space efficiency. In our framework, a learner observes an adversarial positive stream from a target language $K$ and must eventually output a hallucination-free hypothesis language $L \subseteq K$ while omitting at most $\Delta$ strings of $K$. We focus on $\mathcal{C}_{s,k}$, the collection of languages recognized by DFAs with at most $s$ states over an alphabet of size $k$, as the natural hypothesis class for memory-bounded learners. In the exponential-space regime, we prove that a learner can exactly identify the target $K$. Under a stricter memory budget, we characterize the strongest possible generation guarantees. In particular, we present a streaming algorithm using $\mathrm{poly}(s,k)$ space that converges to a hypothesis with generation gap $\Delta = O(k^{2s-2})$. Moreover, the learned hypothesis captures every string in $K$ of length at least $2s-1$. We complement this result with a near-matching lower bound through a reduction from a standard communication complexity problem. Specifically, achieving generation gap $\Delta \le k^{(1-\varepsilon)s}$ requires $k^{\Omega(\varepsilon s)}$ memory. Together, these results reveal a sharp transition between polynomial-space generation and exponential-space exact identification.
Nicolas Flammarion, Chirag Pabbaraju, Hristo Papazov, Miltiadis Stouras, Ola Svensson
COLT3
2025 Learning Algorithms in the Limit
abstract
This paper studies the problem of learning computable functions in the limit by extending Gold’s inductive inference framework to incorporate \textit{computational observations} and \textit{restricted input sources}. Complimentary to the traditional Input-Output Observations, we introduce Time-Bound Observations, and Policy-Trajectory Observations to study the learnability of general recursive functions under more realistic constraints. While input-output observations do not suffice for learning the class of general recursive functions in the limit, we overcome this learning barrier by imposing computational complexity constraints or supplementing with approximate time-bound observations. Further, we build a formal framework around observations of \textit{computational agents} and show that learning computable functions from policy trajectories reduces to learning rational functions from input and output, thereby revealing interesting connections to finite-state transducer inference. On the negative side, we show that computable or polynomial-mass characteristic sets cannot exist for the class of linear-time computable functions even for policy-trajectory observations.
Hristo Papazov, Nicolas Flammarion
COLT1
2024 Leveraging Continuous Time to Understand Momentum When Training Diagonal Linear Networks
abstract
In this work, we investigate the effect of momentum on the optimisation trajectory of gradient descent. We leverage a continuous-time approach in the analysis of momentum gradient descent with step size $\gamma$ and momentum parameter $\beta$ that allows us to identify an intrinsic quantity $\lambda = \frac{ \gamma }{ (1 - \beta)^2 }$ which uniquely defines the optimisation path and provides a simple acceleration rule. When training a $2$-layer diagonal linear network in an overparametrised regression setting, we characterise the recovered solution through an implicit regularisation problem. We then prove that small values of $\lambda$ help to recover sparse solutions. Finally, we give similar but weaker results for stochastic momentum gradient descent. We provide numerical experiments which support our claims.
Hristo Papazov, Scott Pesme, Nicolas Flammarion
AISTATS1