Quoting "Ionut Vancea" <[email protected]>:
from math import e
As a general rule, don't ever directly import anything from math,
numpy, or scipy. Use equivalent definitions from fipy.tools.numerix.
In this case, e**(-faceVar) will not produce at all the same thing as
fipy.tools.numerix.exp(-faceVar).
from fipy.variables.cellVariable import CellVariable
from fipy.tools.numerix import random
var = CellVariable(name = "Simulations",
mesh = mesh,
value = random.random(nx * ny))
faceVar = var.getArithmeticFaceValue()
fDerivative = e**(-faceVar)-(b/(faceVar**3))
OK, this is the problem. fDerivative is a FaceVariable. To get the
proper order for the discretization, you want the second derivative of
f(\phi) to be a FaceVariable, so fDerivative needs to be a
CellVariable. So, either
fDerivative = exp(-var) - (b / var**3)
(h**3 * fDerivative.getFaceGrad()).getDivergence()
or, better,
fSecondDerivative = -exp(-faceVar) + (3 * b / faceVar**4)
DiffusionTerm(coeff=fSecondDerivative)
