Test on an idealized geometry 

Diagnostic equations:
To launch this test, use runme

tests 5 and 6:
A=5.7*10^-19 Pa^-3.a^-1 -> B=1.7687*10^8 Pa.s^1/3

density 5100 -> 1488 grids and 2839 elements
dentity 3550 -> 3221 grids and 6232 elements

the upper boundary condition is now
pos=find(md.y==200000); %grids on the upper boundary condition
md.dirichletvalues_diag(pos,2)=400*(((md.x(pos)-100000)/25000).^2-ones(size(pos,1),1)).*heaviside((1+eps)*ones(size(pos,1),1)-((md.x(pos)-100000)/25000).^2);

We first find all the grids on the upper boundary condition.
Then we modify the velocity in the y direction to model an icestream.
We used 1+eps instead of 1 in the heaiviside function to avoid the case of 0, since Matlab return NaN for the value of 0.
