<div class="gmail_quote">On Thu, Nov 10, 2011 at 11:07, 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=":2jz">1. I use the conservative variables.<br>
<br>
2. No limiter.<br>
<br>
3. Boundary conditions are weakly imposed (to solve the riemann problem).<br>
<br>
4. mat_fd_type ds is worse for the current case<br></div></blockquote><div><br></div><div>It sounds like your system is poorly scaled. If you were consistent about using PetscScalar in your code, then you can configure --with-precision=__float128 and try that. It should remove the differencing errors. It is very important to scale the system carefully when using coloring or matrix-free finite differencing. It's a waste of time to dwell on the other issues until you know that you have an accurate Jacobian.</div>
<div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div id=":2jz"><br>
5. sub_pc_type lu did a better work but not to a satisfactory level<br></div></blockquote><div><br></div><div>In terms of time or iteration count? This test is for iteration count.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div id=":2jz">
<br>
6. MATCOLORINGSL is used.<br>
<br>
For the preconditioner I need to do some changes.<br>
<br>
Please help me first to understand the coloring types in order to choose the best one (any web pages, links etc.?).<br></div></blockquote></div><br>