You're right! I think I must have been trying to process the wrong output file before, so I thought it wasn't producing a solution. The output file does indeed look like the correct solution.

The message is a bit scarey, so I'm glad you changed it.

Many thanks,

- Phil

On Tuesday, March 25, 2014 6:04:12 PM UTC, Robert Cimrman wrote:

Hi Phil,

On 03/25/2014 05:51 PM, seismo_phil wrote:
> Hi,
>
> Thanks for inviting me to contribute usage issues, Robert. I'm using sfepy
> to solve a relatively simple, 2D, thermal diffusion problem.  i can solve
> it useing the following ebcs and equations (i.e., implied zero heat flux at
> left and right boundaries):
>
> ebcs = {
>
> 't1' : ('Gamma_Top', {'t.0' : 0.0}),
>
> 't2' : ('Gamma_Bottom', {'t.0' : 1000.0}),
>
> }
>
>
> equations = {
>
> 'Temperature' : """dw_laplace.2.Omega( coef.val, s, t )
>
> = 0 """
>
> }
>
>
> This works perfectly. I actually need to solve the same problem with an ebc
> at the top but a Neumann boundary condition at the bottom. So I use:
>
>
> ebcs = {
>
> 't1' : ('Gamma_Top', {'t.0' : 0.0}),
>
> }
>
>
> equations = {
>
> 'Temperature' : """dw_laplace.2.Omega( coef.val, s, t )
>
> = dw_surface_integrate.2.Gamma_Bottom(flux.val, s)"""
>
> }
>
>
> where flux is defined in materials as:
>
>
> materials = {
>
>      'flux' : ({'val' : 1.0},),
>
>      'coef' : ({'val' : 1.0},),
>
> }
>
>
> This seems to be exactly like what is done in the example
> poisson_neumann.py But now, I find that the solver fails:
>
>
> sfepy: updating materials...
>
> sfepy:     coef
>
> sfepy:     flux
>
> sfepy: ...done in 0.01 s
>
> sfepy: nls: iter: 0, residual: 9.332878e+04 (rel: 1.000000e+00)
>
> sfepy:   rezidual:    0.00 [s]
>
> sfepy:      solve:    0.00 [s]
>
> sfepy:     matrix:    0.00 [s]
>
> sfepy: linear system not solved! (err = 5.659775e-10 < 1.000000e-10)
>
> sfepy: nls: iter: 1, residual: 5.748516e-10 (rel: 6.159425e-15)
>
>
> I'm confused by this, because I thought that this is still a well-posed
> problem. Can anyone please suggest to me what I may be doing wrong?

The solution is perfectly fine. Look at the sizes of residual norms - the
absolute one is about 5e-10, the relative one about 6e-15, which is as close to
machine precision in double-precision floats as you can get. The message is
just a warning, and it can be prevented by setting the options 'lin_red'  or
'eps_a' of the Newton solver to higher values. There is a check that the linear
system solution error is smaller than (eps_a * lin_red). Anyway, it almost
passes with your settings.

Cheers,
r.