Ranko Lazić
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View article: Benignity of loss landscape with weight decay requires both large overparametrization and initialization
Benignity of loss landscape with weight decay requires both large overparametrization and initialization Open
The optimization of neural networks under weight decay remains poorly understood from a theoretical standpoint. While weight decay is standard practice in modern training procedures, most theoretical analyses focus on unregularized setting…
View article: Learning a Neuron by a Shallow ReLU Network: Dynamics and Implicit Bias for Correlated Inputs
Learning a Neuron by a Shallow ReLU Network: Dynamics and Implicit Bias for Correlated Inputs Open
We prove that, for the fundamental regression task of learning a single neuron, training a one-hidden layer ReLU network of any width by gradient flow from a small initialisation converges to zero loss and is implicitly biased to minimise …
View article: Adversarial Reprogramming Revisited
Adversarial Reprogramming Revisited Open
Adversarial reprogramming, introduced by Elsayed, Goodfellow, and Sohl-Dickstein, seeks to repurpose a neural network to perform a different task, by manipulating its input without modifying its weights. We prove that two-layer ReLU neural…
View article: The Reachability Problem for Two-Dimensional Vector Addition Systems with States
The Reachability Problem for Two-Dimensional Vector Addition Systems with States Open
We prove that the reachability problem for two-dimensional vector addition systems with states is NL-complete or PSPACE-complete, depending on whether the numbers in the input are encoded in unary or binary. As a key underlying technical r…
View article: Human-like Relational Models for Activity Recognition in Video
Human-like Relational Models for Activity Recognition in Video Open
Video activity recognition by deep neural networks is impressive for many classes. However, it falls short of human performance, especially for challenging to discriminate activities. Humans differentiate these complex activities by recogn…
View article: Verifying higher-order concurrency with data automata
Verifying higher-order concurrency with data automata Open
Using a combination of automata-theoretic and game-semantic techniques, we propose a method for analysing higher-order concurrent programs. Our language of choice is Finitary Idealised Concurrent Algol (FICA) due to its relatively simple f…
View article: Leafy Automata for Higher-Order Concurrency
Leafy Automata for Higher-Order Concurrency Open
Finitary Idealized Concurrent Algol (FICA) is a prototypical programming language combining functional, imperative, and concurrent computation. There exists a fully abstract game model of FICA, which in principle can be used to prove equiv…
View article: Leafy automata for higher-order concurrency
Leafy automata for higher-order concurrency Open
Finitary Idealized Concurrent Algol ( $$\mathsf {FICA}$$ ) is a prototypical programming language combining functional, imperative, and concurrent computation. There exists a fully abstract game model of $$\mathsf {FICA}$$ , which in p…
View article: Reachability in fixed dimension vector addition systems with states
Reachability in fixed dimension vector addition systems with states Open
The reachability problem is a central decision problem for formal verification based on vector addition systems with states (VASS), which are equivalent to Petri nets and form one of the most studied and applied models of concurrency. Reac…
View article: KReach: A Tool for Reachability in Petri Nets
KReach: A Tool for Reachability in Petri Nets Open
We present KReach, a tool for deciding reachability in general Petri nets. The tool is a full implementation of Kosaraju’s original 1982 decision procedure for reachability in VASS. We believe this to be the first implementation of its kin…
View article: KReach Artifact - TACAS 2020
KReach Artifact - TACAS 2020 Open
Reproducible outcomes from the 2020 TACAS paper KReach: A Tool for Reachability in Petri Nets by Alex Dixon & Ranko Lazic.
View article: The reachability problem for Petri nets is not elementary
The reachability problem for Petri nets is not elementary Open
Petri nets, also known as vector addition systems, are a long established model of concurrency with extensive applications in modeling and analysis of hardware, software, and database systems, as well as chemical, biological, and business …
View article: Universal trees grow inside separating automata: Quasi-polynomial lower bounds for parity games
Universal trees grow inside separating automata: Quasi-polynomial lower bounds for parity games Open
Several distinct techniques have been proposed to design quasi-polynomial algorithms for solving parity games since the breakthrough result of Calude, Jain, Khoussainov, Li, and Stephan (2017): play summaries, progress measures and registe…
View article: Finkel Was Right: Counter-Examples to Several Conjectures on Variants of Vector Addition Systems (Invited Talk)
Finkel Was Right: Counter-Examples to Several Conjectures on Variants of Vector Addition Systems (Invited Talk) Open
Studying one-dimensional grammar vector addition systems has long been advocated by Alain Finkel. In this presentation, we shall see how research on those systems has led to the recent breakthrough tower lower bound for the reachability pr…
View article: Verification column
Verification column Open
In this accessible yet rigorous column, Christel Baier and Clemens Dubslaff provide a timely and valuable overview of the vibrant area of algorithmic synthesis problems based on Markov decision processes. The latter are one of the most pro…
View article: Verification column
Verification column Open
Any computer scientist who does research in logic and verification will sooner or later cross their path with Presburger arithmetic. This column, authoritatively and accessibly composed by Christoph Haase, fills the gap for a state-of-the-…
View article: When is containment decidable for probabilistic automata
When is containment decidable for probabilistic automata Open
The containment problem for quantitative automata is the natural quantitative generalisation of the classical language inclusion problem for Boolean automata. We study it for probabilistic automata, where it is known to be undecidable in g…
View article: Verification column
Verification column Open
I am honoured to take up the role of the Verification editor for the SIGLOG newsletter, and I am inspired by my predecessor Neha Rungta whose work will be a tough act to follow.
View article: When is Containment Decidable for Probabilistic Automata?
When is Containment Decidable for Probabilistic Automata? Open
The emptiness and containment problems for probabilistic automata are natural quantitative generalisations of the classical language emptiness and inclusion problems for Boolean automata. It is well known that both problems are undecidable…
View article: Succinct progress measures for solving parity games
Succinct progress measures for solving parity games Open
The recent breakthrough paper by Calude et al. has given the first algorithm for solving parity games in quasi-polynomial time, where previously the best algorithms were mildly subexponential. We devise an alternative quasi-polynomial time…
View article: Succinct progress measures for solving parity games
Succinct progress measures for solving parity games Open
The recent breakthrough paper by Calude et al. has given the first algorithm for solving parity games in quasipolynomial time, where previously the best algorithms were mildly subexponential. We devise an alternative quasi-polynomial time …
View article: Perfect half space games
Perfect half space games Open
We introduce perfect half space games, in which the goal of Player 2 is to make the sums of encountered multidimensional weights diverge in a direction which is consistent with a chosen sequence of perfect half spaces (chosen dynamically b…
View article: Polynomial-Space Completeness of Reachability for Succinct Branching VASS in Dimension One
Polynomial-Space Completeness of Reachability for Succinct Branching VASS in Dimension One Open
Whether the reachability problem for branching vector addition systems, or equivalently the provability problem for multiplicative exponential linear logic, is decidable has been a long-standing open question. The one-dimensional case is a…
View article: Reachability in Two-Dimensional Unary Vector Addition Systems with States is NL-Complete
Reachability in Two-Dimensional Unary Vector Addition Systems with States is NL-Complete Open
Blondin et al. showed at LICS 2015 that two-dimensional vector addition systems with states have reachability witnesses of length exponential in the number of states and polynomial in the norm of vectors. The resulting guess-and-verify alg…
View article: A polynomial-time algorithm for reachability in branching VASS in dimension one
A polynomial-time algorithm for reachability in branching VASS in dimension one Open
Branching VASS (BVASS) generalise vector addition systems with states by allowing for special branching transitions that can non-deterministically distribute a counter value between two control states. A run of a BVASS consequently becomes…
View article: A Polynomial-Time Algorithm for Reachability in Branching VASS in Dimension One
A Polynomial-Time Algorithm for Reachability in Branching VASS in Dimension One Open
Branching VASS (BVASS) generalise vector addition systems with states by allowing for special branching transitions that can non-deterministically distribute a counter value between two control states. A run of a BVASS consequently becomes…
View article: Reachability in Two-Dimensional Unary Vector Addition Systems with States is NL-Complete
Reachability in Two-Dimensional Unary Vector Addition Systems with States is NL-Complete Open
Blondin et al. showed at LICS 2015 that two-dimensional vector addition systems with states have reachability witnesses of length exponential in the number of states and polynomial in the norm of vectors. The resulting guess-and-verify alg…
View article: Reachability in Two-Dimensional Unary Vector Addition Systems with\n States is NL-Complete
Reachability in Two-Dimensional Unary Vector Addition Systems with\n States is NL-Complete Open
Blondin et al. showed at LICS 2015 that two-dimensional vector addition\nsystems with states have reachability witnesses of length exponential in the\nnumber of states and polynomial in the norm of vectors. The resulting\nguess-and-verify …