doc(pytorch): update docs/pytorch.md (#649)

Co-authored-by: zhulin.zzz <zhul289@chinaunicom.cn>

docs/pytorch.md

@@ -198,6 +198,41 @@ torch.Size([1, 2, 28])                  # 参数代表在哪里添加维度    0
 torch.Size([2, 28, 1])
 ```
 
+Cuda 相关
+---
+### 检查 Cuda 是否可用
+```python
+>>> import torch.cuda
+>>> torch.cuda.is_available()
+>>> True
+```
+### 列出 GPU 设备
+```python
+import torch
+device_count = torch.cuda.device_count()
+print("CUDA 设备")
+for i in range(device_count):
+    device_name = torch.cuda.get_device_name(i)
+    total_memory = torch.cuda.get_device_properties(i).total_memory / (1024 ** 3)
+    print(f"├── 设备 {i}: {device_name}, 容量: {total_memory:.2f} GiB")
+print("└── (结束)")
+```
+### 将模型、张量等数据在 GPU 和内存之间进行搬运
+```python
+import torch
+# Replace 0 to your GPU device index. or use "cuda" directly.
+device = f"cuda:0"
+# Move to GPU
+tensor_m = torch.tensor([1, 2, 3])
+tensor_g = tensor_m.to(device)
+model_m = torch.nn.Linear(1, 1)
+model_g = model_m.to(device)
+# Move back.
+tensor_m = tensor_g.cpu()
+model_m = model_g.cpu()
+```
+
+
 导入 Imports
 ---