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.