Model Details
Table | |
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| Base model | Qwen/Qwen2.5-1.5B-Instruct |
| Architecture | Causal decoder-only LM |
| Fine-tuning method | QLoRA (4-bit base, LoRA r=16, α=32) — merged into base weights for this release |
| Trainable parameters at training time | ~18.5M (LoRA adapter only) |
| Training data | BanglaParaphrase, 100,000-pair subset |
| Max sequence length | 512 tokens |
| Effective batch size | 16 |
| Early stopping | Stopped at step 2,700 (43% of planned 6,250 steps); validation loss re-confirmed on the full 5K validation set (0.411) |
| Trained on | Google Colab (free-tier T4 GPU) |
| License | Apache 2.0 (matches base model) |
Trained on a single free-tier Colab T4 GPU with early stopping (43% of planned steps); despite the reduced training budget, this model achieved the highest surface-overlap metrics of the four — though not the most semantically reliable, see Evaluation Results.
Intended Use
Generating Bengali paraphrases of an input sentence — e.g., data augmentation for downstream Bengali NLP tasks, or research on low-resource paraphrase generation and parameter-efficient fine-tuning. Evaluated only on the BanglaParaphrase test distribution; not evaluated on other domains, dialects, or languages.
Out-of-Scope Use
- Not intended for languages other than Bengali, or for code-mixed/transliterated text.
- Not suitable for unreviewed automated use. This model had the highest hallucination rate of all four models studied (22/100 judged examples) — see Sample Outputs for a real failure case. Do not deploy outputs from this model without human review in any context where factual or semantic accuracy matters.
- Not a general-purpose Bengali instruction-following or chat model — although built on an instruction-tuned base, this checkpoint is fine-tuned specifically for sentence-level paraphrasing and has not been evaluated for other tasks.
How to Use
from transformers import AutoModelForCausalLM, AutoTokenizer
model_name = "AvinabhDutta-Dev/bangla-paraphrase-qwen2.5-qlora"
tokenizer = AutoTokenizer.from_pretrained(model_name)
model = AutoModelForCausalLM.from_pretrained(model_name, torch_dtype="auto", device_map="auto")
text = "এই বাড়িতে সাধারণত কোনো ঝগড়াঝাঁটি হয় না।"
messages = [{"role": "user", "content": f"Paraphrase this Bengali sentence: {text}"}]
inputs = tokenizer.apply_chat_template(messages, add_generation_prompt=True, return_tensors="pt")
output_ids = model.generate(inputs, max_new_tokens=160, do_sample=False)
print(tokenizer.decode(output_ids[0][inputs.shape[-1]:], skip_special_tokens=True))
Sample Outputs
Real outputs from this model on the held-out test set — one strong example and one genuine failure case, both from the study's LLM-judge evaluation, shown here deliberately for transparency rather than only showcasing favorable results:
Good paraphrase (judge: meaning 5/5, fluency 5/5):
Table with columns: Source, Generated| Source | Generated |
|---|
| কিন্তু আসলেই কি সবাই অভাগা? | কিন্তু সবাই কি অভাগা? |
Hallucination failure case (judge: meaning 1/5, fluency 2/5):
Table with columns: Source, Generated| Source | Generated |
|---|
| কিছু সরকারি কর্মকর্তা আছে যারা আমার কাছ থেকে প্রতিবছর গরু নিতো। | আমাদের প্রতিবছর গরু নিতে হবে কিছু সরকারি কর্মকর্তা। |
Judge's assessment: "The generated text distorts the original meaning completely and has poor grammar." The source describes officials taking cows from the speaker; the generated output garbles both the grammar and the direction of the action.
Evaluation Results
Evaluated on the full, held-out BanglaParaphrase test set (23,332 examples), using the same pipeline and test data across all four models in this study.
Table with columns: Metric, Score| Metric | Score |
|---|
| BLEU | 12.71 |
| ROUGE-L | 0.377 |
| BERTScore (F1, BanglaBERT) | 0.923 |
| PINC (lexical novelty vs. source) | 0.773 |
For context: a 70B-class zero-shot LLM baseline reported on this same dataset in prior work scores in the 10–12 BLEU range — this fine-tuned 1.5B model performs comparably despite being over an order of magnitude smaller, using only ~18.5M trainable parameters (~1.2% of the model's total).
LLM-as-a-Judge Validation
A 400-pair, four-model symmetric subset (100 examples per model, identical sources) was independently scored by Gemini 3.5 Flash-Lite on semantic meaning preservation and fluency (1–5 scale), with a binary meaning-reversal flag.
Table with columns: Metric, Score| Metric | Score |
|---|
| Mean judge meaning-preservation score | 3.72 / 5 |
| Mean judge fluency score | 3.84 / 5 |
Error breakdown (out of 100 judged examples):
Table with columns: Category, Count| Category | Count |
|---|
| Valid paraphrase | 69 |
| Hallucination / semantic drift | 22 |
| Meaning reversal | 4 |
| Severe disfluency | 5 |
Limitations
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This model had the highest hallucination rate of all four models in the study (22/100 judged examples), despite scoring best on automated overlap metrics (BLEU, ROUGE-L, BERTScore). See Sample Outputs above for a real, representative failure case. This is a concrete illustration of why this study cross-validates automated metrics against LLM-judge scoring: strong surface-overlap metrics do not guarantee semantic reliability.
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Training-time validation loss was originally logged against a reduced 500-example subset for eval-frequency efficiency; a full-5K re-evaluation confirmed this was an accurate proxy (0.4113 vs. 0.4109).
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Trained on a 100K-example subset (not the full ~420K available training pairs) and evaluated with greedy decoding, for compute tractability.
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BLEU/ROUGE-L are known to correlate only weakly with actual paraphrase quality; this model is the clearest example of that gap in this study — high overlap scores, but the highest semantic-error rate under human-proxy review.
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Reproducibility: Trained on a fixed 100,000-pair subset of BanglaParaphrase with a documented train/val/test split (see processed_data/metadata.json in the GitHub repo); decoding was fully deterministic (greedy, do_sample=False), so generation outputs are reproducible given the same checkpoint and inputs.
Citation
If you use this model, please cite both the original Qwen2.5/BanglaParaphrase work and this study:
@misc{qwen2.5,
title = {Qwen2.5: A Party of Foundation Models},
url = {https://qwenlm.github.io/blog/qwen2.5/},
author = {Qwen Team},
month = {September},
year = {2024}
}
@misc{banglaparaphrase2022,
title={BanglaParaphrase: A High-Quality Bengali Paraphrase Dataset},
author={Akil, Ajwad and others},
year={2022}
}
See the project GitHub repository for the full paper, code, and citation for this study.
Framework Versions
- Transformers 5.13.1
- PEFT 0.19.1 (used during training; adapter merged into base weights for this release)
license: apache-2.0