Thoughts Are All Over the Place: On the Underthinking of Long Reasoning Models - Wang, Yue; Liu, Qiuzhi; Xu, Jiahao; Liang, Tian; Chen, Xingyu; He, Zhiwei; Song, Linfeng; Yu, Dian; Li, Juntao; Zhang, Zhuosheng; Wang, Rui; Tu, Zhaopeng; et al. (Advances in Neural Information Processing Systems, 2025)