Plotting subdomain with FiPy

show.py

import fipy as fp

L = 12
nx = 200.
ny = nx
dx = L/nx
dy = L/ny
mesh = fp.Grid2D(nx=nx, ny=ny, dx=dx, dy=dy) + [[-L/2]]

x, y = mesh.getCellCenters()
X, Y = mesh.faceCenters

phi = fp.CellVariable(name = "solution variable",
                      mesh = mesh,
                      value = x * y)

width = L / 2.

viewer = fp.Viewer(vars=phi,
                   limits={'xmin': -width / 2, 'xmax': width / 2, 'ymin': -width / 2, 'ymax': width / 2, 'datamax': 4.})

viewer.plot()

raw_input('stopped')