For my thesis i have to expand the derich algorithm to the 4th order.

In the example of Recursive gaussian there is deriche method of the second order but not of 3rd of 4th order.

So my question to you guys is, how can i make a 3rd order deriche with this code?

I dont see also not the logic behind the deriche code if i run the code i get the follwing results

***for order 0: a1 + a2 + a3 + a4 != 0 (is this true)

***for order 1 & 2: a1 + a2 + a3 + a4 = 0 (is this coincidence)
also the sum of coefp & coefn is equal to 0 ???

I want to understand the logic behind this code. How the values of the coefficients (b0 b1 a1 a2 a3 a4) are calculate. I looked up many papers/google/CImg/etc, but i cant find any information about those coefficients.