Questions about the implementation of Grad-CAM++: The second and third order derivatives

[hxngu]

#541 When I try to learn how to get hessian matrix I find the implementation of Grad-CAM++ just used grads_power_2 = grads**2 and grads_power_3 = grads_power_2 * grads to get the second and third order derivatives. Is that correct? The formula in original paper is listed below.

[caihuaiguang]

GradCAM++ approximates second and third-order derivatives using squared and cubed gradients, which holds only when logits are passed through an exponential function (i.e., output = exp(logits) ).

Computing the exact Hessian matrix is both time-consuming and space-consuming. However, obtaining the Hessian-vector product requires only a single backward pass, as demonstrated in ShapleyCAM, which is also merged to this repository.