[Add] matrix_exp docs (#6414)

docs/api/paddle/linalg/Overview_cn.rst

@@ -41,6 +41,7 @@ paddle.linalg 目录下包含飞桨框架支持的线性代数相关 API。具
     " :ref:`paddle.linalg.inv <cn_api_paddle_linalg_inv>` ", "计算方阵的逆矩阵"
     " :ref:`paddle.linalg.pinv <cn_api_paddle_linalg_pinv>` ", "计算矩阵的广义逆"
     " :ref:`paddle.linalg.cov <cn_api_paddle_linalg_cov>` ", "计算矩阵的协方差矩阵"
+    " :ref:`paddle.linalg.matrix_exp <cn_api_paddle_linalg_matrix_exp>` ", "计算方阵的矩阵指数"
 
 
 .. _about_matrix_decompositions:

docs/api/paddle/linalg/matrix_exp_cn.rst

@@ -0,0 +1,32 @@
+.. _cn_api_paddle_linalg_matrix_exp:
+
+matrix_exp
+-------------------------------
+
+.. py:function:: paddle.linalg.matrix_exp(x, name=None)
+
+计算方阵的矩阵指数。
+
+.. math::
+
+    exp(A) = \sum_{n=0}^\infty A^n/n!
+
+输入的张量 ``x`` 应该是方阵，比如 ``(*, M, M)`` ，矩阵指数通过比例平方法的帕德近似计算而来。
+
+[1] Nicholas J. Higham, The scaling and squaring method for the matrix exponential revisited.
+
+
+参数
+::::::::::::
+
+    - **x** (Tensor) - 输入张量，形状应该为 ``(*, M, M)`` ， ``*`` 表示 0 或多个维度。数据类型为： ``float32``, ``float64`` 。
+    - **name** (str，可选) - 具体用法请参见 :ref:`api_guide_Name`，一般无需设置，默认值为 None。
+
+返回
+::::::::::::
+Tensor，与 ``x`` 的类型和形状相同。
+
+代码示例
+::::::::::
+
+COPY-FROM: paddle.linalg.matrix_exp

docs/guides/model_convert/convert_from_pytorch/api_difference/linalg/torch.linalg.matrix_exp.md

@@ -0,0 +1,20 @@
+## [ 仅参数名不一致 ]torch.linalg.matrix_exp
+### [torch.linalg.matrix_power](https://pytorch.org/docs/stable/generated/torch.linalg.matrix_exp.html#torch.linalg.matrix_exp)
+
+```python
+torch.linalg.matrix_exp(A)
+```
+
+### [paddle.linalg.matrix_exp](https://www.paddlepaddle.org.cn/documentation/docs/zh/develop/api/paddle/linalg/matrix_exp_cn.html)
+
+```python
+paddle.linalg.matrix_exp(x, name=None)
+```
+
+Pytorch 相比 Paddle 仅参数名不一致，具体如下：
+
+### 参数映射
+
+| PyTorch       | PaddlePaddle | 备注                                                   |
+| ------------- | ------------ | ------------------------------------------------------ |
+| A          |  x           | 输入的方阵，类型为 Tensor,仅参数名不一致。  |

docs/guides/model_convert/convert_from_pytorch/pytorch_api_mapping_cn.md

@@ -1537,6 +1537,7 @@
 | ----- | ----------- | ----------------- | --- |
 | REFERENCE-MAPPING-ITEM(`torch.linalg.svd`, https://github.com/PaddlePaddle/docs/tree/develop/docs/guides/model_convert/convert_from_pytorch/api_difference/linalg/torch.linalg.svd.md) |
 | REFERENCE-MAPPING-ITEM(`torch.linalg.matrix_power`, https://github.com/PaddlePaddle/docs/tree/develop/docs/guides/model_convert/convert_from_pytorch/api_difference/linalg/torch.linalg.matrix_power.md) |
+| REFERENCE-MAPPING-ITEM(`torch.linalg.matrix_exp`, https://github.com/PaddlePaddle/docs/tree/develop/docs/guides/model_convert/convert_from_pytorch/api_difference/linalg/torch.linalg.matrix_exp.md) |
 | REFERENCE-MAPPING-ITEM(`torch.linalg.cholesky`, https://github.com/PaddlePaddle/docs/tree/develop/docs/guides/model_convert/convert_from_pytorch/api_difference/linalg/torch.linalg.cholesky.md) |
 | REFERENCE-MAPPING-ITEM(`torch.linalg.matrix_rank`, https://github.com/PaddlePaddle/docs/tree/develop/docs/guides/model_convert/convert_from_pytorch/api_difference/linalg/torch.linalg.matrix_rank.md) |
 | REFERENCE-MAPPING-ITEM(`torch.linalg.cross`, https://github.com/PaddlePaddle/docs/tree/develop/docs/guides/model_convert/convert_from_pytorch/api_difference/linalg/torch.linalg.cross.md) |