PhD Visiting Program at University of Novi Sad

In today’s interconnected global society, the value of international experiences in expanding one’s
horizons is highly recognized among students and researchers who are dedicated to their academic
pursuits. For me, it was an exceptional opportunity to venture into a new academic environment
when I embarked on a three-month visiting program at the University of Novi Sad (UNS) in Serbia.

My name is Mahsa Yousefi, and I am a Persian Ph.D. mathematics student at the University of Trieste
in Italy. Taking advantage of my university’s policy that permits research periods abroad for visiting
junior researchers, I seized the chance to dedicate a portion of my thesis study to the Department of
Mathematics and Informatics (DMI) at UNS from November 2022 to January 2023. Throughout my
visit, I was hosted by Prof. Natasa Krejic and collaborated closely with Prof. Natasa Krklec Jerinkic,
both of whom impressed me with their professionalism and unwavering dedication to our work. Our
primary focus revolved around research directly connected to my Ph.D. thesis, specifically exploring
second-order optimization methods like limited memory quasi-Newton methods to tackle nonlinear
non-convex optimization problems that arise in training deep neural networks (DNNs), such as image
classification problems. During my time at UNS, we developed and established the convergence
properties of a method called ASNTR, which incorporates an adaptive subsampling scheme within
subsampled non-monotone trust-region methods for training DNNs. Notably, this method requires
fewer gradient evaluations compared to its counterpart known as STORM.

In addition to doing research, I participated in the department’s weekly seminars at DMI. These
sessions were really interesting for me in the sense of a friendly atmosphere, students and
researchers updated each other by their recent activities. In my opinion, every department should
have such sessions. I also communicated with a number of welcome students and got familiar with
some other experts in my research domain. These connections hold the potential for future
partnerships beyond the scope of my Ph.D.

From the moment I arrived in Novi Sad until the day I departed, I found it to be a lovely city with
warm and hospitable residents. Being a nature enthusiast, I was captivated by the beauty of the fall
and winter seasons. The charming Danube River, which was conveniently located near my place of
residence, further immersed me in the enchanting surroundings. While I have never considered
myself particularly fortunate, this visiting program served as a reminder that I should reconsider my

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