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Rishikesh Gajjala

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3

SAT Conference 2025 Conference Paper

CNFs and DNFs with Exactly k Solutions

  • L. Sunil Chandran
  • Rishikesh Gajjala
  • Kuldeep S. Meel

Model counting is a fundamental problem that consists of determining the number of satisfying assignments for a given Boolean formula. The weighted variant, which computes the weighted sum of satisfying assignments, has extensive applications in probabilistic reasoning, network reliability, statistical physics, and formal verification. A common approach for solving weighted model counting is to reduce it to unweighted model counting, which raises an important question: What is the minimum number of terms (or clauses) required to construct a DNF (or CNF) formula with exactly k satisfying assignments? In this paper, we establish both upper and lower bounds on this question. We prove that for any natural number k, one can construct a monotone DNF formula with exactly k satisfying assignments using at most O(√{log k}log log k) terms. This construction represents the first o(log k) upper bound for this problem. We complement this result by showing that there exist infinitely many values of k for which any DNF or CNF representation requires at least Ω(log log k) terms or clauses. These results have significant implications for the efficiency of model counting algorithms based on formula transformations.

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MFCS Conference 2024 Conference Paper

Krenn-Gu Conjecture for Sparse Graphs

  • L. Sunil Chandran
  • Rishikesh Gajjala
  • Abraham M. Illickan

Greenberger–Horne–Zeilinger (GHZ) states are quantum states involving at least three entangled particles. They are of fundamental interest in quantum information theory, and the construction of such states of high dimension has various applications in quantum communication and cryptography. Krenn, Gu and Zeilinger discovered a correspondence between a large class of quantum optical experiments which produce GHZ states and edge-weighted edge-coloured multi-graphs with some special properties called the GHZ graphs. On such GHZ graphs, a graph parameter called dimension can be defined, which is the same as the dimension of the GHZ state produced by the corresponding experiment. Krenn and Gu conjectured that the dimension of any GHZ graph with more than 4 vertices is at most 2. An affirmative resolution of the Krenn-Gu conjecture has implications for quantum resource theory. Moreover, this would save huge computational resources used for finding experiments which lead to higher dimensional GHZ states. On the other hand, the construction of a GHZ graph on a large number of vertices with a high dimension would lead to breakthrough results. In this paper, we study the existence of GHZ graphs from the perspective of the Krenn-Gu conjecture and show that the conjecture is true for graphs of vertex connectivity at most 2 and for cubic graphs. We also show that the minimal counterexample to the conjecture should be 4-connected. Such information could be of great help in the search for GHZ graphs using existing tools like PyTheus. While the impact of the work is in quantum physics, the techniques in this paper are purely combinatorial, and no background in quantum physics is required to understand them.

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