### Abstract

In this paper we study the computational complexity of the *Upward Planarity Extension* problem, which takes in input an upward planar drawing $\Gamma_H$ of a subgraph $H$ of a directed graph $G$ and asks whether $\Gamma_H$ can be extended to an upward planar drawing of $G$. Our study fits into the line of research on the extensibility of partial representations, which has recently become a mainstream in Graph Drawing.

We show the following results.

- First, we prove that the
*Upward Planarity Extension* problem is NP-complete, even if $G$ has a prescribed upward embedding, the vertex set of $H$ coincides with the one of $G$, and $H$ contains no edge. - Second, we show that the
*Upward Planarity Extension* problem can be solved in $O(n \log n)$ time if $G$ is an $n$-vertex upward planar $st$-graph. This result improves upon a known $O(n^2)$-time algorithm, which however applies to all $n$-vertex single-source upward planar graphs. - Finally, we show how to solve in polynomial time a surprisingly difficult version of the
*Upward Planarity Extension* problem, in which $G$ is a directed path or cycle with a prescribed upward embedding, $H$ contains no edges, and no two vertices share the same $y$-coordinate in $\Gamma_H$.

Publication

In *16th International Symposium on Algorithms and Data Structures (WADS 2019)*

###### Assistant Professor (RTDb)

My research interests are in Algorithm Engineering and Complexity, focused in particular on the theoretical and algorithmic challenges arising from the visualization of graphs.