Paper:
The loss landscapes of deep neural networks are poorly understood due to their high nonconvexity. Empirically, the local minima of these loss functions can be connected by a learned curve in model space, along which the loss remains nearly constant. Yet, current path finding algorithms do not consider the influence of symmetry in the loss surface caused by weight permutations of the networks corresponding to the minima. We propose a framework to investigate the effect of symmetry on landscape connectivity by directly optimizing the weight permutations of the networks being connected. To learn a locally optimal permutation, we introduce a proximal alternating minimization scheme and prove some convergence guarantees. Using an neuron alignment technique, we derive an inexpensive heuristic for approximating a locally optimal weight permutation. Empirically, optimizing the permutation is critical for efficiently learning a simple, planar, low-loss curve between networks that successfully generalizes. As an application, we also show that there is a performance gain, particularly for models with less parameters, in the accuracy of ensembles constructed from the learned curve with neuron alignment permutation.

Review:
The paper investigates the connection between symmetries in the neural network architectures and the loss landscape of the corresponding neural networks. In the previous works, there was shown that the two local minima of a neural network can be connected by a curve with the low validation/train loss along the curve. Despite the loss on the curve being close to the loss at the end points, there are segments of the curve on which the loss in higher than loss at the local minima. To overcome this problem, the authors proposed two-step procedure: 1. Align weights between two neural networks 2. Launch the path finding algorithm between aligned weights. In other words, the authors proposed to connect not original local minima but local minima that parametrize the same functions as the original ones, but have a different order of neurons. The authors also proposed PAM algorithm where they iteratively apply path finding algorithm and weights alignment algorithm.
Novelty and significance. The idea to combine the symmetrization of NN architectures with path finding algorithms is new to the best of my knowledge. Experimentally, the authors showed that ensembling the midpoint and endpoints of the curve found via path finding  algorithm coupled with the neural alignment algorithm delivers a better result than simple averaging of three independent networks. This is a new and significant result, since before the ensembling of points along the curve had the same quality as the ensemble of three independent networks or marginally better.  
The weak side of the paper is the PAM algorithm that occupies a significant part of the paper and does not deliver a significantly better result than the simple application of the neural alignment procedure before launching the path finding algorithm.
Clarity. Overall, the related work section contains all relevant references to the previous works to the best of my knowledge. The paper is well written, excluding the section Neuron Alignment that lacks notation description.  
The paper contains several typos and inaccuracies:
1. “However, We find its empirical performance is similar to standard curve finding, and we advocate the latter for practical use due to computational efficiency.” The word “We” should start with the lowercase letter.
2. In the sentence “The first question to address is how to effectively deal with the constraints in equation 6” the index i should be replaced with the index l.
3. Notation Π|Kl| introduced after equation 5.
4. In the section describing neuron alignment  algorithm Lie et al. [1] used a different notation. So I would recommend to further extend this section and add all necessary notations. Also, I would recommend to add a direct link to the paper where the problem is described in matrix form.
5. In the Algorithm 1 “Initialize P θ2 := [Wˆ 2 1 ,Wˆ 2 2 , ...,Wˆ 2 L ] as [W2 1 ,W2 2 , ...,W2 L ] for k ∈ {1, 2, ..., L − 1};”  k is not used anywhere in notation.
6. In Figure 3, “model 2 aligned ” sing is out of the plot box for ResNet-32 and VGG-16 architectures.
7. The appendix contains the sketch of the proof that is quite difficult to follow. I would recommend giving all necessary definitions as it is done in the [2] and extend the proof. 
Overall, it is quite an interesting paper but it contains some drawbacks.
[1] Yixuan Li, Jason Yosinski, Jeff Clune, Hod Lipson, and John E Hopcroft.  Convergent learning: Do different neural networks learn the same representations?  In ICLR, 2016
[2]  H́edy Attouch, J́erˆome Bolte, Patrick Redont, and Antoine Soubeyran.  Proximal alternating minimization and projection methods for nonconvex problems:  An approach based on the kurdyka-łojasiewicz inequality.Mathematics of Operations Research, 35(2):438–457, 2010