Function rprop_step 

pub fn rprop_step<T: Triton, const BLOCK_SIZE: i32>(
    params_ptr: T::Pointer<f32>,
    grad_ptr: T::Pointer<f32>,
    prev_grad_ptr: T::Pointer<f32>,
    step_size_ptr: T::Pointer<f32>,
    n_elements: i32,
    eta_plus: f32,
    eta_minus: f32,
    step_min: f32,
    step_max: f32,
)
where
    T::I32Tensor: Tensor<i32, 1> + Comparison<i32, BoolTensor = T::BoolTensor>,
    T::Pointer<f32>: AddOffsets<i32, 1, T::I32Tensor, Output = T::Tensor<T::Pointer<f32>>>,

Rprop step (resilient backpropagation).

sign      = g * prev_g          (product of current and previous gradient)
step_size = step_size * eta_plus   if sign > 0
          = step_size * eta_minus  if sign < 0
          = step_size              otherwise
step_size = clamp(step_size, step_min, step_max)
g_masked  = 0                    if sign < 0 (gradient reversal: skip update)
          = g                    otherwise
p        -= sign(g_masked) * step_size
prev_g    = g_masked

Grid: [ceil(n_elements / BLOCK_SIZE), 1, 1].