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+---
+title: MMDDatasetEvaluator
+createTime: 2025/04/04 19:46
+permalink: /en/api/operators/text_sft/eval/mmddatasetevaluator/
+---
+
+## 📘 Overview
+
+The `MMDDatasetEvaluator` is an operator that evaluates the distribution discrepancy between two datasets using the Maximum Mean Discrepancy (MMD) method. It embeds text into a high-dimensional space and computes the kernel-based distance to quantify the distribution shift between the evaluation dataset and a reference dataset. A smaller MMD score indicates that the two distributions are closer.
+
+## `__init__`
+
+```python
+def __init__(
+    self,
+    ref_frame: DataFlowStorage,
+    *,
+    ref_max_sample_num: int = 5000,
+    ref_shuffle_seed: int = 42,
+    ref_instruction_key: str = "input",
+    ref_output_key: str = "output",
+    kernel_type: Literal["RBF"] = "RBF",
+    bias: bool = True,
+    rbf_sigma: float = 1.0,
+    embedding_type: Literal["vllm", "sentence_transformers"] = "sentence_transformers",
+    embedding_model_name: str | None = None,
+    st_device: str = "cuda",
+    st_batch_size: int = 32,
+    st_normalize_embeddings: bool = True,
+    vllm_max_num_seqs: int = 128,
+    vllm_gpu_memory_utilization: float = 0.9,
+    vllm_tensor_parallel_size: int = 1,
+    vllm_pipeline_parallel_size: int = 1,
+    vllm_truncate_max_length: int = 40960,
+    cache_type: Literal["redis", "none"] = "none",
+    redis_url: str = "redis://127.0.0.1:6379",
+    max_concurrent_requests: int = 50,
+    redis_db: int = 0,
+    cache_model_id: str | None = None,
+)
+```
+
+| Parameter | Type | Default | Description |
+| :--- | :--- | :--- | :--- |
+| **ref_frame** | DataFlowStorage | Required | The reference dataset used as the distribution baseline. |
+| **ref_max_sample_num** | int | `5000` | Maximum number of samples to draw from the reference dataset. |
+| **ref_shuffle_seed** | int | `42` | Random seed for sampling the reference dataset. |
+| **ref_instruction_key** | str | `'input'` | Column name for the instruction field in the reference dataset. |
+| **ref_output_key** | str | `'output'` | Column name for the output field in the reference dataset. |
+| **kernel_type** | str | `'RBF'` | Kernel function type; currently only `'RBF'` is supported. |
+| **bias** | bool | `True` | Whether to use bias in the MMD computation. |
+| **rbf_sigma** | float | `1.0` | Bandwidth parameter for the RBF kernel. |
+| **embedding_type** | str | `'sentence_transformers'` | Embedding backend to use; either `'sentence_transformers'` or `'vllm'`. **Note:** when using `'vllm'`, you need to install `distflow[vllm]` first. |
+| **embedding_model_name** | str | Required | Name of the embedding model (required). |
+| **st_device** | str | `'cuda'` | Device for SentenceTransformers (e.g., `'cuda'`, `'cpu'`). |
+| **st_batch_size** | int | `32` | Batch size for SentenceTransformers inference. |
+| **st_normalize_embeddings** | bool | `True` | Whether to normalize embeddings from SentenceTransformers. |
+| **vllm_max_num_seqs** | int | `128` | Maximum number of sequences for vLLM. |
+| **vllm_gpu_memory_utilization** | float | `0.9` | GPU memory utilization ratio for vLLM. |
+| **vllm_tensor_parallel_size** | int | `1` | Tensor parallel size for vLLM. |
+| **vllm_pipeline_parallel_size** | int | `1` | Pipeline parallel size for vLLM. |
+| **vllm_truncate_max_length** | int | `40960` | Maximum truncation length for vLLM inputs. |
+| **cache_type** | str | `'none'` | Cache type for embeddings; either `'redis'` or `'none'`. |
+| **redis_url** | str | `'redis://127.0.0.1:6379'` | Redis connection URL when `cache_type='redis'`. |
+| **max_concurrent_requests** | int | `50` | Maximum concurrent requests to Redis. |
+| **redis_db** | int | `0` | Redis database index. |
+| **cache_model_id** | str | `None` | Model identifier used for the Redis cache key. |
+
+## `run`
+
+```python
+def run(
+    self,
+    storage: DataFlowStorage,
+    input_instruction_key: str,
+    input_output_key: str,
+    max_sample_num: int | None = None,
+    shuffle_seed: int | None = None,
+) -> tuple[float, dict[str, Any]]
+```
+
+| Parameter | Type | Default | Description |
+| :--- | :--- | :--- | :--- |
+| **storage** | DataFlowStorage | Required | The DataFlowStorage instance containing the evaluation dataset. |
+| **input_instruction_key** | str | Required | Column name for the instruction field in the evaluation dataset. |
+| **input_output_key** | str | Required | Column name for the output field in the evaluation dataset. |
+| **max_sample_num** | int | `None` | Maximum samples from the evaluation dataset; falls back to `ref_max_sample_num` if not set. |
+| **shuffle_seed** | int | `None` | Random seed for sampling the evaluation dataset; falls back to `ref_shuffle_seed` if not set. |
+
+## 🧠 Example Usage
+
+```python
+from dataflow.operators.text_sft.eval import MMDDatasetEvaluator
+from dataflow.utils.storage import FileStorage
+
+# Prepare reference and evaluation storages
+ref_storage = FileStorage(first_entry_file_name="reference_data.jsonl")
+eval_storage = FileStorage(first_entry_file_name="eval_data.jsonl")
+
+# Initialize the evaluator
+evaluator = MMDDatasetEvaluator(
+    ref_frame=ref_storage.step(),
+    ref_instruction_key="instruction",
+    ref_output_key="output",
+    embedding_type="sentence_transformers",
+    embedding_model_name="BAAI/bge-large-zh",
+    st_device="cuda",
+    st_batch_size=32,
+)
+
+# Run evaluation
+mmd_score, mmd_meta = evaluator.run(
+    eval_storage.step(),
+    input_instruction_key="instruction",
+    input_output_key="output",
+)
+print(f"MMD Score: {mmd_score}, Meta: {mmd_meta}")
+```
+
+#### 🧾 Default Output Format
+
+| Field | Type | Description |
+| :--- | :--- | :--- |
+| **MMDScore** | float | The computed MMD distance (smaller is closer). |
+| **MMDMeta** | dict | Metadata dictionary containing computation details. |
+
+**Example Output:**
+```json
+{
+  "MMDScore": 0.00342,
+  "MMDMeta": {
+    "num_src_samples": 5000,
+    "num_tgt_samples": 5000
+  }
+}
+```
diff --git a/docs/zh/notes/api/operators/text_sft/eval/MMDDatasetEvaluator.md b/docs/zh/notes/api/operators/text_sft/eval/MMDDatasetEvaluator.md
new file mode 100644
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@@ -0,0 +1,142 @@
+---
+title: MMDDatasetEvaluator
+createTime: 2025/04/04 19:46
+permalink: /zh/api/operators/text_sft/eval/mmddatasetevaluator/
+---
+
+## 📘 概述
+
+[MMDDatasetEvaluator](https://github.com/OpenDCAI/DataFlow/blob/main/dataflow/operators/text_sft/eval/mmd_dataset_evaluator.py) 是一个基于最大均值差异（Maximum Mean Discrepancy, MMD）的数据集评估算子。它通过将文本嵌入到高维空间，并计算核函数距离，来量化评估数据集与参考数据集之间的分布偏移程度。MMD 值越小，表示两个数据集的分布越接近。
+
+## `__init__`
+
+```python
+def __init__(
+    self,
+    ref_frame: DataFlowStorage,
+    *,
+    ref_max_sample_num: int = 5000,
+    ref_shuffle_seed: int = 42,
+    ref_instruction_key: str = "input",
+    ref_output_key: str = "output",
+    kernel_type: Literal["RBF"] = "RBF",
+    bias: bool = True,
+    rbf_sigma: float = 1.0,
+    embedding_type: Literal["vllm", "sentence_transformers"] = "sentence_transformers",
+    embedding_model_name: str | None = None,
+    st_device: str = "cuda",
+    st_batch_size: int = 32,
+    st_normalize_embeddings: bool = True,
+    vllm_max_num_seqs: int = 128,
+    vllm_gpu_memory_utilization: float = 0.9,
+    vllm_tensor_parallel_size: int = 1,
+    vllm_pipeline_parallel_size: int = 1,
+    vllm_truncate_max_length: int = 40960,
+    cache_type: Literal["redis", "none"] = "none",
+    redis_url: str = "redis://127.0.0.1:6379",
+    max_concurrent_requests: int = 50,
+    redis_db: int = 0,
+    cache_model_id: str | None = None,
+)
+```
+
+### init 参数说明
+
+| 参数名 | 类型 | 默认值 | 说明 |
+| :--- | :--- | :--- | :--- |
+| **ref_frame** | DataFlowStorage | 必需 | 参考数据集（DataFlowStorage），作为分布比较的基准。 |
+| **ref_max_sample_num** | int | `5000` | 从参考数据集中采样的最大样本数。 |
+| **ref_shuffle_seed** | int | `42` | 参考数据集采样的随机种子。 |
+| **ref_instruction_key** | str | `'input'` | 参考数据集中指令字段的列名。 |
+| **ref_output_key** | str | `'output'` | 参考数据集中输出字段的列名。 |
+| **kernel_type** | str | `'RBF'` | 核函数类型，当前仅支持 `'RBF'`。 |
+| **bias** | bool | `True` | 是否在 MMD 计算中使用偏置项。 |
+| **rbf_sigma** | float | `1.0` | RBF 核函数的带宽参数。 |
+| **embedding_type** | str | `'sentence_transformers'` | 嵌入模型后端，可选 `'sentence_transformers'` 或 `'vllm'`。**注意：** 使用 `'vllm'` 时需先安装 `distflow[vllm]`。 |
+| **embedding_model_name** | str | 必需 | 嵌入模型名称（必填）。 |
+| **st_device** | str | `'cuda'` | SentenceTransformers 的运行设备（如 `'cuda'`、`'cpu'`）。 |
+| **st_batch_size** | int | `32` | SentenceTransformers 的推理批次大小。 |
+| **st_normalize_embeddings** | bool | `True` | 是否对 SentenceTransformers 生成的嵌入向量进行归一化。 |
+| **vllm_max_num_seqs** | int | `128` | vLLM 的最大序列数。 |
+| **vllm_gpu_memory_utilization** | float | `0.9` | vLLM 的 GPU 显存利用率。 |
+| **vllm_tensor_parallel_size** | int | `1` | vLLM 的张量并行大小。 |
+| **vllm_pipeline_parallel_size** | int | `1` | vLLM 的流水线并行大小。 |
+| **vllm_truncate_max_length** | int | `40960` | vLLM 输入的最大截断长度。 |
+| **cache_type** | str | `'none'` | 嵌入缓存类型，可选 `'redis'` 或 `'none'`。 |
+| **redis_url** | str | `'redis://127.0.0.1:6379'` | 使用 Redis 缓存时的连接地址。 |
+| **max_concurrent_requests** | int | `50` | 对 Redis 缓存的最大并发请求数。 |
+| **redis_db** | int | `0` | Redis 数据库索引。 |
+| **cache_model_id** | str | `None` | Redis 缓存键中使用的模型标识符。 |
+
+## `run`
+
+```python
+def run(
+    self,
+    storage: DataFlowStorage,
+    input_instruction_key: str,
+    input_output_key: str,
+    max_sample_num: int | None = None,
+    shuffle_seed: int | None = None,
+) -> tuple[float, dict[str, Any]]
+```
+
+执行算子主逻辑，从评估数据集中读取样本，计算其与参考数据集之间的 MMD 距离，并返回距离值和元数据。
+
+#### 参数
+
+| 名称 | 类型 | 默认值 | 说明 |
+| :--- | :--- | :--- | :--- |
+| **storage** | DataFlowStorage | 必需 | 包含评估数据集的数据流存储实例。 |
+| **input_instruction_key** | str | 必需 | 评估数据集中指令字段的列名。 |
+| **input_output_key** | str | 必需 | 评估数据集中输出字段的列名。 |
+| **max_sample_num** | int | `None` | 评估数据集的最大采样数；未设置时默认使用 `ref_max_sample_num`。 |
+| **shuffle_seed** | int | `None` | 评估数据集采样的随机种子；未设置时默认使用 `ref_shuffle_seed`。 |
+
+## 🧠 示例用法
+
+```python
+from dataflow.operators.text_sft.eval import MMDDatasetEvaluator
+from dataflow.utils.storage import FileStorage
+
+# 准备参考数据集和评估数据集
+ref_storage = FileStorage(first_entry_file_name="reference_data.jsonl")
+eval_storage = FileStorage(first_entry_file_name="eval_data.jsonl")
+
+# 初始化评估器
+evaluator = MMDDatasetEvaluator(
+    ref_frame=ref_storage.step(),
+    ref_instruction_key="instruction",
+    ref_output_key="output",
+    embedding_type="sentence_transformers",
+    embedding_model_name="BAAI/bge-large-zh",
+    st_device="cuda",
+    st_batch_size=32,
+)
+
+# 执行评估
+mmd_score, mmd_meta = evaluator.run(
+    eval_storage.step(),
+    input_instruction_key="instruction",
+    input_output_key="output",
+)
+print(f"MMD Score: {mmd_score}, Meta: {mmd_meta}")
+```
+
+#### 🧾 默认输出格式
+
+| 字段 | 类型 | 说明 |
+| :--- | :--- | :--- |
+| **MMDScore** | float | 计算得到的 MMD 距离值（越小表示分布越接近）。 |
+| **MMDMeta** | dict | 包含计算细节信息的元数据字典。 |
+
+**示例输出：**
+```json
+{
+  "MMDScore": 0.00342,
+  "MMDMeta": {
+    "num_src_samples": 5000,
+    "num_tgt_samples": 5000
+  }
+}
+```