Function hessians

Constructs the Hessian of sum of `ys` with respect to `x` in `xs`. `hessians()` adds ops to the graph to output the Hessian matrix of `ys` with respect to `xs`. It returns a list of `Tensor` of length `len(xs)` where each tensor is the Hessian of `sum(ys)`. The Hessian is a matrix of seco

(ys,
             xs,
             name="hessians",
             colocate_gradients_with_ops=False,
             gate_gradients=False,
             aggregation_method=None)