HanGyeol Yoo

Author directory

Also published as: Hangyeol Yoo


2026

This paper introduces DocPlan, a vision-language training dataset designed to emulate the stepwise reasoning strategies employed by human during visual document understanding. DocPlan was constructed to enable vision-language models (VLMs) to effectively learn the structured reasoning process that humans typically follow when interpreting documents. We reorganized existing document understanding datasets into 133K examples annotated with the following four sequential stages: Recognition → Planning → Extraction and Reasoning → Conclusion. To evaluate the effectiveness of DocPlan, we fine-tuned the direct prediction-based VLMs to perform stepwise reasoning generation across these stages. The experimental results demonstrated that our approach achieved up to a 34.4% improvement in accuracy on document-based benchmarks.
We introduce KFinEval, a benchmark for evaluating large language models (LLMs) in the Korean financial domain, with about 1K expert-curated instances across foundational financial knowledge, regulation-grounded procedural reasoning under noisy contexts, and financial toxicity under adversarial prompts. Existing financial benchmarks are largely English-centric and emphasize numerical or surface reasoning, providing limited coverage of regulation-grounded decision-making and domain-specific safety. Evaluating proprietary and open-weight LLMs, we observe substantial disparities and trade-offs among knowledge accuracy, procedural reasoning, and safety-aligned behavior; notably, strong capability does not consistently translate into safer responses under adversarial financial scenarios. KFinEval provides a practical Korean-regulation-grounded benchmark for diagnosing and improving financial LLM reliability and safety. Code and resources: https://github.com/sklim84/KFinEval.
Building effective tokenizers for multilingual Large Language Models (LLMs) requires careful control over language-specific data mixtures. While a tokenizer’s compression performance critically affects the efficiency of LLM training and inference, existing approaches rely on heuristics or costly large-scale searches to determine optimal language ratios. We introduce Tokenizer Regression for Optimal Data MiXture (TReX), a regression-based framework that efficiently predicts the optimal data mixture for tokenizer training. TReX trains small-scale proxy tokenizers on random mixtures, gathers their compression statistics, and learns to predict compression performance from data mixtures. This learned model enables scalable mixture search before large-scale tokenizer training, mitigating the accuracy-cost trade-off in multilingual tokenizer design. Tokenizers trained with TReX’s predicted mixtures outperform mixtures based on LLaMA3 and uniform distributions by up to 12% in both in- and out-of-distribution compression efficiency, demonstrating strong scalability, robustness, and practical effectiveness.
We propose an efficient layer-specific optimization (ELO) method designed to enhance continual pretraining (CP) for specific languages in multilingual large language models (MLLMs). This approach addresses the common challenges of high computational cost and degradation of source language performance associated with traditional CP. The ELO method consists of two main stages: (1) ELO Pretraining, where a small subset of specific layers, identified in our experiments as the critically important first and last layers, are detached from the original MLLM and trained with the target language. This significantly reduces not only the number of trainable parameters but also the total parameters computed during the forward pass, minimizing GPU memory consumption and accelerating the training process. (2) Layer Alignment, where the newly trained layers are reintegrated into the original model, followed by a brief full fine-tuning step on a small dataset to align the parameters. Experimental results demonstrate that the ELO method achieves a training speedup of up to 6.46 times compared to existing methods, while improving target language performance by up to 6.2% on qualitative benchmarks and effectively preserving source language (English) capabilities.

2025

This study explores the integration of automated writing evaluation (AWE) and grammatical error correction (GEC) through multitask learning, demonstrating how combining these distinct tasks can enhance performance in both areas. By leveraging a shared learning framework, we show that models trained jointly on AWE and GEC outperform those trained on each task individually. To support this effort, we introduce a dataset specifically designed for multitask learning using AWE and GEC. Our experiments reveal significant synergies between tasks, leading to improvements in both writing assessment accuracy and error correction precision. This research represents a novel approach for optimizing language learning tools by unifying writing evaluation and correction tasks, offering insights into the potential of multitask learning in educational applications.

2024

The impressive development of large language models (LLMs) is expanding into the realm of large multimodal models (LMMs), which incorporate multiple types of data beyond text. However, the nature of multimodal models leads to significant expenses in the creation of training data. Furthermore, constructing multilingual data for LMMs presents its own set of challenges due to language diversity and complexity. Therefore, in this study, we propose two cost-effective methods to solve this problem: (1) vocabulary expansion and pretraining of multilingual LLM for specific languages, and (2) automatic and elaborate construction of multimodal datasets using GPT4-V. Based on these methods, we constructed a 91K English-Korean-Chinese multilingual, multimodal training dataset. Additionally, we developed a bilingual multimodal model that exhibits excellent performance in both Korean and English, surpassing existing approaches.