Hi the board

I've now a problem that i cant solve for many days on derivative vector

I've installed Eigen librairy and then i put some CSV data to a dynamic matrix, this part works
I can also find maximum of column, and parse the matrix with eigen::arithmeticsequence ( it was no more installed on 3.3.7...it was little hard to manage) but now i can do it

The problem is that i have to make a derivative of vector on another vector i will give sample example

matrix A 3x3 : 1 2 3
4 5 4
5 6 7

i have to make derivative 1st colum on third : like (5-1)/(7-3)
The problem i need to make it as sequence with (n-(n-2))/ (n-(n-2)) in automatic sequence...
I cant find any function in eigen to make easy derivative.... that's easy to sum ou minus column but cell by cell i cant solve any idea ?!