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EMA（Exponential Moving Average，指数移动平均）是一种常用的数据平滑算法，它通过对最近的数据点赋予更高的权重，来减少数据的波动性，从而更清晰地观察数据的趋势变化。
在 Ant Design Charts 的实现中，EMA 的计算方式如下：
其中：
⚠️ 注意：Ant Design Charts 中 EMA 的实现与传统定义中的 α 权重位置相反，因此：
α越接近 1，平滑效果越明显；α越接近 0，EMA 越接近原始数据。
| 属性 | 描述 | 类型 | 默认值 | 是否必选 |
|---|---|---|---|---|
| field | 需要平滑的字段名 | string | 'y' | ✓ |
| alpha | 平滑因子，控制平滑程度（越大越平滑） | number | 0.6 | |
| as | 生成的新字段名，若不指定将覆盖原字段 | string | 同 field |
若需保留原字段，建议设置
as属性以输出到新字段。 该默认值由组件内部定义，非来源于主题。 ⚠️ 注意：field字段必须为数值型，否则将导致计算错误。
以下示例展示如何在 Ant Design Charts 中对数据字段 close 应用 EMA 平滑变换。
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