Some confusions about the main code

[QuantummyKnight]

B = N-curvature(i).*(L.*x0+M.y0);
C = curvature(i).(x0.^2+y0.^2);
delta = C./(B+sqrt(B.^2-curvature(i).*C));
Hello! Sorry to trouble you. I wonder the meaning of the ''B,C,delta'' and how can I learn about the fomulas. Are there any books introducing them? Looking forward to your reply.