How to compute the jacobian
 

Hi: Friends, i am developing a code for the solution of the heat conduction in complex region using the finite volume method. and the computation was conducted in the computation region. As we know, the coefficient for the fist node (i,2) near the boundary is as follows:

AJM(i,2)=B22(i,1)*gam(i,1)/jacoban(i,1) where B22 is a coefficient which can be found in the Peric's book. But i don't know how to compute the jacobian(i,1) at the boundary. please help me. Regards