Define random values through expression

2

Hi, f=Expression(“g”, g=g, degree=1) should be thought of as defining f such that f(x)=g(x). In ran_mu_expr=Expression(“ran_mu”,ran_mu=ran_mu, degree=4) you seem to make an assumption that Expression will do the lookup in ran_mu array to assign the coefficient value appropriately. That is not the case. Consider instead

from dolfin import *
import numpy as np


class RandomScalar(UserExpression):
    def eval(self, value, x):
        value[:] = np.random.rand()
    def value_shape(self, ):
        return ()

    
def fill_random0(f):
    f.assign(interpolate(RandomScalar(degree=1), f.function_space()))
    return f


def fill_random1(f):
    f.vector().set_local(np.random.rand(f.vector().local_size()))
    return f
# To illustrate speed difference
for n in (64, 128, 256):
    mesh = UnitSquareMesh(n, n)
    V = FunctionSpace(mesh, 'CG', 1)
    f = Function(V)
    print('n=%d' % n)
    for fill in (fill_random0, fill_random1):
        t = Timer()
        fill(f)
        print('\t', t.stop())

# Expression using function
mesh = UnitSquareMesh(n, n)
V = FunctionSpace(mesh, 'CG', 1)

f = Function(V)
# Randomize
f = fill_random1(f)

f_expr = Expression('f', f=f, degree=1)
print(sqrt(abs(assemble(inner(f-f_expr, f-f_expr)*dx))))