# create linear solver
ksp = PETSc.KSP()
ksp.create(PETSc.COMM_WORLD)
# use conjugate gradients
ksp.setType('cg')
# and incomplete Cholesky
# (only for PETSc with complex number support)
#ksp.getPC().setType('icc')
# obtain sol & rhs vectors
x, b = A.createVecs()
x.set(0)
b.set(1)
# and next solve
ksp.setOperators(A)
ksp.setFromOptions()
ksp.solve(b, x)