Subtracting two CellFunctions

ASubB_cells.py

from dolfin import *
import numpy

mesh = UnitSquare(8, 8)

# Creating two mesh functions, empty to start with....
a = CellFunction("double", mesh)
b = CellFunction("double", mesh)
result = CellFunction("double", mesh)

# initializing mesh functions
# a.set_all(0.00)
# b.set_all(0.00)
# result.set_all(0.00)

# create two numpy arrays... 
na1 = numpy.arange(20, dtype = 'd')
na2 = numpy.ones(50)

a.set_values(na1)
b.set_values(na2)

# Doing operation on the data
# for cell in cells(mesh):
# 	result[cell] = a[cell] - b[cell]

# method to do the subtraction operation
def subtract(a,b,result):
	temp_result = a.array() - b.array()
	return result.set_values(temp_result)

# calling the subtraction method
subtract(a,b,result)

print "The type of result:"
type(result)
info(result, True)

#info(cell_marker2, True)

# plot(cell_marker2, interactive=True)

# plot(mesh, interactive=True)