Problem in Boundary Integration

Hi,

I am having some issues with the command POSTINT. I am tyring to solve a much more complex problem than outlined in the attached document. However, if somebody can point out what is the issue in the sample problem attched, I can go figure out the issue in my original problem.

3
==============\
|*********************\
|****del^u=0*********\ 4 (u=1)
|***********************\
| 1 (u=0) *************/
|**********************/ 5 (u=1)
|********************/
=============/
2


I am solving Laplace's equation in the above 2D-domain where all the edges except 1,4 and 5 are insulated. Thus the current density (=-del(u)) when integrated over any boundary edge should give me the total current passing through the edge. I use:

% Current passing into the system through edges 4 and 5

v1 = postint(fem,'-(ux*(-nx)+uy*(-ny))','dl',[4,5],'edim',1)

% Current passing out of the system through edge 1

v2 = postint(fem,'-(ux*(nx)+uy*(ny))','dl',[1],'edim',1)

Since the edges 3 and 2 are insulated (i.e. del(u)=0), and the gometry is symmetric I should expect v1 = v2. But I get,

v1 = 0.8553
v2 = 0.8776

Why this discrepancy ? I have attached the code for your perusal and also the results.

Regards
Murali