Bug in how to defined the mid-points

j_mid = (numpy.shape(T)[0]+1)/2
i_mid = (numpy.shape(T)[1]+1)/2 are not the mids point
for example if T is 5x5 then (j_mid, i_mid) = (3,3) according to the definition and
should be (2,2) cause the indeces go from 0 to 4. So the +1 shouldn't be there..

In the case of nx=ny even we don't have a mid point but we have to choose one, so it will work without the +1.