# tensorplay.func.hessian

Source: https://www.tensorplay.cn/docs/generated/tensorplay.func.hessian.html

```python
tensorplay.func.hessian(func: Callable, argnums: int | tuple[int, ...] = 0)
```

Returns a function computing the Hessian of func.

Built as the reverse-mode jacobian of the reverse-mode gradient.  The
forward-over-reverse ordering would need tangents to flow through the
backward pass itself, which this engine’s reverse mode does not carry;
reverse-over-reverse composes two plain jacobians instead.

Example

```
>>> def f(x):
...     return x.sin().sum()
>>> hess = hessian(f)(tensorplay.randn(5))
>>> hess.shape
tensorplay.Size(5, 5)
```