About Lucas-Kanade optical flow method

I'm trying to code Lucas-Kanade method by following the help document https://www.mathworks.com/help/vision/ref/opticalflowlk.html?s_tid=srchtitle

I have some questions about the algorithm details:

1. In the step "Compute between images 1 and 2 using the kernel", does this equals to ?
2. In the step "Smooth the gradient components", is the isotropic 5-by-5 element kernel computed by ?
3. In the final step's case 2: and , for a specific pixel, could someone show me an example on how to normalize the gradient flow?

Thanks.