Converting symbols to UFL type

1

Hi, I have a problem when I try to solve a Nonlinear Varational problem, specifically when trying to compute the varational part with a coefficient depending on x,y and u:

# Packages used
from __future__ import print_function
from fenics import *
import matplotlib.pyplot as plt
import numpy as np
################################################################
# Defining Relativity hydraulic conductivity
# Defining k_s(x), positive function.
def k_s(x,y):
    return 0.1+10*(sin(20*(x))*sin(20*y)+1)
# Haverkamp model
# Constants used
A=1
B=1
Gamma=1

def k(x,y,u):
    return k_s(x,y)*(A/(A+((abs(u)/B)**Gamma)))
    
# Use SymPy to compute f from the manufactured solution u

import sympy as sym
x, y = sym.symbols('x[0], x[1]')

u = 2*x**2+y*y+4*x
f = - sym.diff(k(x,y,u)*sym.diff(u, x), x) -sym.diff(k(x,y,u)*sym.diff(u, y), y)
f = sym.simplify(f)
u_code = sym.printing.ccode(u)
f_code = sym.printing.ccode(f)
print('u =', u_code)
print('f =', f_code)

u = sin(x*2*pi)
f = - sym.diff(k(x,y,u)*sym.diff(u, x), x) -sym.diff(k(x,y,u)*sym.diff(u, y), y)
f = sym.simplify(f)
u_code = sym.printing.ccode(u)
f_code = sym.printing.ccode(f)
print('u =', u_code)
print('f =', f_code)

I get the following compilation error:

    Traceback (most recent call last):
      File "muestra.py", line 25, in <module>
        f = - sym.diff(k(x,y,u)*sym.diff(u, x), x) -sym.diff(k(x,y,u)*sym.diff(u, y), y)
      File "muestra.py", line 19, in k
        return k_s(x,y)*(A/(A+((abs(u)/B)**Gamma)))
      File "muestra.py", line 10, in k_s
        return 0.1+10*(sin(20*(x))*sin(20*y)+1)
      File "/usr/lib/python3/dist-packages/ufl/operators.py", line 598, in sin
        return _mathfunction(f, Sin)
      File "/usr/lib/python3/dist-packages/ufl/operators.py", line 569, in _mathfunction
        f = as_ufl(f)
      File "/usr/lib/python3/dist-packages/ufl/constantvalue.py", line 413, in as_ufl
        " to any UFL type." % str(expression))
    ufl.log.UFLValueError: Invalid type conversion: 20*x[0] can not be converted to any UFL type.

Thank you in advance for helping me

2

You are mixing UFL with sympy objects, in particular, sin in your code is the one from UFL.