*If switch is set to -yes, then the moment of the unknowns
with respect to the middle of the post_line (same index)
is calculated (instead of the average value of the unknowns).
This moment is the integral of the unknown value multiplied
with the distance to the middle of the line multiplied by the area
contribution; the first point in the post_line has negative
distance with respect to the line middle and the second point
in the post_line has positive distance with respect
to the line middle.
*

tochnog 2001-09-02