Hello

I want to calculate the condition number of **stiffness matrix** in nonlinear Poisson equation. I followed this post. Here is the minimal example:

```
from dolfin import *
import numpy as np
# Sub domain for Dirichlet boundary condition
class DirichletBoundary(SubDomain):
def inside(self, x, on_boundary):
return abs(x[0] - 1.0) < DOLFIN_EPS and on_boundary
# Create mesh and define function space
mesh = UnitSquareMesh(32, 32)
V = FunctionSpace(mesh, "CG", 1)
# Define boundary condition
g = Constant(1.0)
bc = DirichletBC(V, g, DirichletBoundary())
# Define variational problem
u = Function(V)
v = TestFunction(V)
f = Expression("x[0]*sin(x[1])",degree=1)
F = inner((1 + u**2)*grad(u), grad(v))*dx - f*v*dx
# Compute solution
solve(F == 0, u, bc)
A = assemble(lhs(F))
print (np.linalg.cond(A.array()))
```

I am expecting to get the condition number of the stiffness matrix but it returns this error:

```
print (np.linalg.cond(A.array()))
AttributeError: 'float' object has no attribute 'array'
```

I am just wondering how I can get it done. Any help is appreciated.

Best