## [ 组合替代实现 ]torch.Tensor.is_pinned
### [torch.Tensor.is\_pinned](https://docs.pytorch.org/docs/stable/generated/torch.Tensor.is_pinned.html#torch.Tensor.is_pinned)
```python
torch.Tensor.is_pinned()
```

返回张量是否在固定内存上; Paddle 无此 API，需要组合实现。

### 转写示例
```python
# PyTorch 写法
y = a.is_pinned(b)

# Paddle 写法
y = 'pinned' in str(a.place)
```
