<div class="gmail_quote">On Tue, Nov 1, 2011 at 12:01, Konstantinos Kontzialis <span dir="ltr"><<a href="mailto:ckontzialis@lycos.com">ckontzialis@lycos.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div id=":o4">1. I use 3.1 version of petsc.<br></div></blockquote><div><br></div><div>please upgrade to 3.2 when you can</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div id=":o4">
2. I run the problem with snes_fd and pc_type lu<br>
3. I use a nondimensional form of the NS equations<br>
4. I do not specify any user defined procedure for applying the preconditioner. I leave petsc to deal with this.<br>
<br>
With snes_fd I got the following results:<br>
<br>
Timestep 0: dt = 0.002, T = 0, Res[rho] = 1.06871e-16, Res[rhou] = 0.00215523, Res[rhov] = 1.61374e-08, Res[E] = 6.17917e-07, CFL = 399.998<div class="im"><br>
<br>
/*********************Stage 1 of SSPIRK (6,4)******************/<br>
<br></div>
0 SNES Function norm 1.153030915909e-02<br>
0 KSP preconditioned resid norm 1.153030915909e-02 true resid norm 1.153030915909e-02 ||A||/||Ax|| 1.000000000000e+00<br>
1 KSP preconditioned resid norm 1.998438714390e-11 true resid norm 1.998438714940e-11 ||Ae||/||Ax|| 1.733204797344e-09<div class="im"><br>
Linear solve converged due to CONVERGED_RTOL iterations 1<br></div>
1 SNES Function norm 1.908346652619e-08<br>
0 KSP preconditioned resid norm 1.908346652619e-08 true resid norm 1.908346652619e-08 ||Ae||/||Ax|| 1.000000000000e+00<br>
1 KSP preconditioned resid norm 1.407495233141e-08 true resid norm 2.936727417791e-08 ||Ae||/||Ax|| 1.538885722759e+00<br>
2 KSP preconditioned resid norm 1.983096664116e-16 true resid norm 4.111894600521e-03 ||Ae||/||Ax|| 2.154689555421e+05<br></div></blockquote><div><br></div><div>This looks like a singular preconditioner. Suggest checking the implementation of boundary conditions. Also try -ksp_type fgmres.</div>
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div id=":o4">My function for computing the residual of the system has the following form:<br>
<br>
F(u) = Mu + R(u),<br>
<br>
where M is the mass matrix of the system and R(u) the residual and u is the solution.</div></blockquote><div><br></div><div>This does not look right. I would expect</div><div><br></div><div>M udot = R_u(u,p)</div><div>0 = R_p(u)</div>
</div>