# How to calculate the bandwidth of the Diks and Panchenko(2006) nonlinear granger causality test?

I am doing the nonlinear causality test of the crude oil futures and spot prices, and I want to use the method introduced by Diks and Panchenko(2006), but I am confused about how to choose the optimal bandwidth. I learned it can be calculated from the ARCH(1) process, but I don't know how to get the C here (𝜀𝑛=𝑚𝑎𝑥(𝐶−2/7𝑛,1.5)). I hope you can help me with this. Thank you very much