I have three functions: f_1, f_2, and f_3.
I want to construct the matrix A for the following linear system:
so the first line of the system will be f_2(x_1) + f_3(x_2) = q_1
second line will be f_1(x_1) + f_2(x_2) + f_3(x_3) = q_2
third line f_1(x_2) + f_2(x_3) + f_3(x_4) = q_3
and so on.