using System;
public partial class roots{

public static void bmatrix
(Func<vector,vector> f,vector x,matrix B,double dx=1e-8){
	int n=x.size;
	vector fx=f(x);
	for(int i=0;i<n;i++){
		x[i]+=dx;
		vector df=f(x)-fx;
		for(int j=0;j<n;j++) B[i,j]=dx/df[j];
		x[i]-=dx;
		}
}

}//class