e-mail: nikolentzos at lix.polytechnique dot fr |

I am a Postdoctoral researcher at the Computer Science Laboratory (LIX), École Polytechnique, France.

I received my PhD in Graph Mining from the Athens University of Economics and Business where I was advised by Prof. Michalis Vazirgiannis. Before that, I obtained an MSc in Artificial Intelligence from the University of Southampton and a Diploma in Electrical and Computer Engineering from the University of Patras.

My current research interests are in the fields of learning on graphs and of graph-based information extraction.

**Synthetic electronic health records generated with variational graph autoencoders**

G. Nikolentzos, M. Vazirgiannis, C. Xypolopoulos, M. Lingman, and E.G. Brandt.

npj Digital Medicine, Volume 6, No. 1, (2023) [Impact factor: 15.357].

**Predicting COVID-19 positivity and hospitalization with multi-scale graph neural networks**

K. Skianis, G. Nikolentzos, B. Gallix, R. Thiebaut, and G. Exarchakis.

Scientific Reports, Volume 13, No. 1, (2023) [Impact factor: 4.997].

**Geometric Random Walk Graph Neural Networks via Implicit Layers** [pdf] [code]

G. Nikolentzos and M. Vazirgiannis.

In Proceedings of the 26th International Conference on Artificial Intelligence and Statistics, pp. 2035-2053, 2023.

**Weisfeiler and Leman go Hyperbolic: Learning Distance Preserving Node Representations** [pdf] [code]

G. Nikolentzos, M. Chatzianastasis and M. Vazirgiannis.

In Proceedings of the 26th International Conference on Artificial Intelligence and Statistics, pp. 1037-1054, 2023.

**Graph Alignment Kernels using Weisfeiler and Leman Hierarchies** [pdf] [code]

G. Nikolentzos and M. Vazirgiannis.

In Proceedings of the 26th International Conference on Artificial Intelligence and Statistics, pp. 2019-2034, 2023.

**Permute Me Softly: Learning Soft Permutations for Graph Representations** [pdf] [code]

G. Nikolentzos, G. Dasoulas and M. Vazirgiannis.

IEEE Transactions on Pattern Analysis and Machine Intelligence, Volume 45, No. 4, pp. 5087-5098, (2023) [Impact factor: 24.314].

**Graph Kernels: A Survey** [pdf]

G. Nikolentzos, G. Siglidis and M. Vazirgiannis.

Journal of Artificial Intelligence Research, Volume 72, pp. 943-1027, (2021).

**An Empirical Study of the Expressiveness of Graph Kernels and Graph Neural Networks**

G. Nikolentzos, G. Panagopoulos and M. Vazirgiannis.

In Proceedings of the 30th International Conference on Artificial Neural Networks, pp. 139-150, 2021.

**Ego-Based Entropy Measures for Structural Representations on Graphs**

G. Dasoulas, G. Nikolentzos, K. Scaman, A. Virmaux and M. Vazirgiannis.

In Proceedings of the 2021-2021 IEEE International Conference on Acoustics, Speech and Signal Processing, pp. 3210-3214, 2021.

**Transfer Graph Neural Networks for Pandemic Forecasting** [pdf] [code]

G. Panagopoulos, G. Nikolentzos and M. Vazirgiannis.

In Proceedings of the 35th AAAI Conference on Artificial Intelligence, pp. 4838-4845, 2021.

**Random Walk Graph Neural Networks** [pdf] [code]

G. Nikolentzos and M. Vazirgiannis.

In Proceedings of the 34th Conference on Neural Information Processing Systems, pp. 16211-16222, 2020.

**Image Classification Using Graph-Based Representations and Graph Neural Networks**.

G. Nikolentzos, M. Thomas, A.R. Rivera and M. Vazirgiannis.

In Proceedings of the 9th International Conference on Complex Networks and Their Applications, pp. 142-153, 2020.

**Graph Auto-Encoders for Learning Edge Representations**.

V. Rennard, G. Nikolentzos and M. Vazirgiannis.

In Proceedings of the 9th International Conference on Complex Networks and Their Applications, pp. 117-129, 2020.

**EvoNet: A Neural Network for Predicting the Evolution of Dynamic Graphs**.

C. Wu, G. Nikolentzos and M. Vazirgiannis.

In Proceedings of the 29th International Conference on Artificial Neural Networks, pp. 596-606, 2020.

**k-hop Graph Neural Networks** [code]

G. Nikolentzos, G. Dasoulas and M. Vazirgiannis.

Neural Networks, Volume 130, pp. 195-205, (2020) [Impact factor: 5.535].

**Rep the Set: Neural Networks for Learning Set Representations**. [pdf] [code]

K. Skianis, G. Nikolentzos, S. Limnios and M. Vazirgiannis.

In Proceedings of the 23rd International Conference on Artificial Intelligence and Statistics, pp. 1410-1420, 2020.

**GraKeL: A Graph Kernel Library in Python**. [pdf]

G. Siglidis, G. Nikolentzos, S. Limnios, C. Giatsidis, K. Skianis and M. Vazirgiannis.

Journal of Machine Learning Research 21 (2020) [Impact factor: 4.091].

**Message Passing Attention Networks for Document Understanding**. [code]

G. Nikolentzos, A. Tixier and M. Vazirgiannis.

In Proceedings of the 34th AAAI Conference on Artificial Intelligence, pp. 8544-8551, 2020.

**Learning Structural Node Representations using Graph Kernels**. [pdf] [code]

G. Nikolentzos, M. Vazirgiannis.

IEEE Transactions on Knowledge and Data Engineering, Volume 33, Issue 5, pp. 2045-2056, (2021) [Impact factor: 3.857].

**Matching Node Embeddings Using Valid Assignment Kernels**.

C. Wu, G. Nikolentzos and M. Vazirgiannis.

In Proceedings of the 8th International Conference on Complex Networks and Their Applications (Volume 1), pp. 810-821, 2019.

**Graph Classification with 2D Convolutional Neural Networks**.

A. Tixier, G. Nikolentzos, P. Meladianos and M. Vazirgiannis.

In Proceedings of the 28th International Conference on Artificial Neural Networks: Workshop and Special Sessions, pp. 578-593, 2019.

**Rooted Citation Graphs Density Metrics for Research Papers Influence Evaluation**.

C. Giatsidis, G. Nikolentzos, C. Zhang, J. Tang and M. Vazirgiannis.

Journal of Informetrics 13 (2019) 757-768 [Impact factor: 3.879].

**Learning Structural Node Representations on Directed Graphs**.

N. Steenfatt, G. Nikolentzos, M. Vazirgiannis and Q. Zhao.

In Proceedings of the 7th International Conference on Complex Networks and Their Applications, pp. 132-144, 2018.

**Enhancing Graph Kernels via Successive Embeddings**.

G. Nikolentzos and M. Vazirgiannis.

In Proceedings of the 27th International Conference on Information and Knowledge Management, pp. 1583-1586, 2018.

**Kernel Graph Convolutional Neural Networks**.

G. Nikolentzos, P. Meladianos, A. Tixier, K. Skianis and M. Vazirgiannis.

In Proceedings of the 27th International Conference on Artificial Neural Networks, pp. 22-32, 2018.

**A Degeneracy Framework for Graph Similarity**. [pdf] [code]

G. Nikolentzos, P. Meladianos, S. Limnios and M. Vazirgiannis.

In Proceeding of the 27th International Joint Conference on Artificial Intelligence, pp. 2595-2601, 2018.

**An Optimization Approach for Sub-event Detection and Summarization in Twitter**. [pdf]

P. Meladianos, C. Xypolopoulos, G. Nikolentzos and M. Vazirgiannis.

In Proceedings of the 40th European Conference on Information Retrieval, pp. 481-493, 2018.

**Shortest-Path Graph Kernels for Document Similarity**. [code]

G. Nikolentzos, P. Meladianos, F. Rousseau, Y. Stavrakas and M. Vazirgiannis.

In Proceedings of the 2017 Conference on Empirical Methods in Natural Language Processing, pp. 1890-1900, 2017.

**K-clique-graphs for Dense Subgraph Discovery**.

G. Nikolentzos, P. Meladianos, Y. Stavrakas and M. Vazirgiannis.

In Proceedings of the 2017 European Conference on Machine Learning and Principles and Practice of Knowledge Discovery, pp. 617-633, 2017.

**Real-Time Keyword Extraction from Conversations**.

P. Meladianos, A. Tixier, G. Nikolentzos and M. Vazirgiannis.

In Proceedings of the 15th Conference of the European Chapter of the Association for Computational Linguistics, pp. 462-467, 2017.

**Multivariate Gaussian Document Representation from Word Embeddings for Text Categorization**. [code]

G. Nikolentzos, P. Meladianos, F. Rousseau, Y. Stavrakas and M. Vazirgiannis.

In Proceedings of the 15th Conference of the European Chapter of the Association for Computational Linguistics, pp. 450-455, 2017.

**Matching Node Embeddings for Graph Similarity.** [pdf] [code]

G. Nikolentzos, P. Meladianos and M. Vazirgiannis.

In Proceedings of the 31st AAAI Conference on Artificial Intelligence, pp. 2429-2435, 2017.

**Degeneracy-based Real-Time Sub-Event Detection in Twitter Stream**.

P. Meladianos, G. Nikolentzos, F. Rousseau, Y. Stavrakas and M. Vazirgiannis.

In Proceedings of the 9th AAAI International Conference on Web and Social Media, pp. 248-257, 2015.

**AUEB at TREC 2015: Clinical Decision Support Track**.

G. Nikolentzos, P. Meladianos, N. Liakis and M. Vazirgiannis.

In Proceedings of TREC 2015.

**KAGNNs: Kolmogorov-Arnold Networks meet Graph Learning**. [pdf]

R. Bresson, G. Nikolentzos, G. Panagopoulos, M. Chatzianastasis, J. Pang and M. Vazirgiannis.

arXiv, 2024.

I have been a teaching assistant in the following courses at AUEB:

and in the following course at École Polytechnique:

- Advanced Learning for Text and Graph Data (ALTeGraD)

GraKeL: A library for graph kernels

- Benchmark Data Sets for Graph Kernels
- Stanford Large Network Dataset Collection
- UCI Machine Learning Repository

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