where is defined over a region in d dimensional space---d=2 in text as one can draw.
Figure: FEM 1
Let
with on
and a function of over d dimensional
is defined over a region 
in d
dimensional space---d=2 in text as one can draw.
is fixed =f on boundary 
of
(Figure FEM 1)
Figure: FEM 1
on 
a function of 
over d dimensional 