<div>Hi,</div>
<div> </div>
<div>just to clarify. I'm using structured grid but not cartesian ie strictly horizontal/vertical. So I can't DA, can I?</div>
<div> </div>
<div>But can I use DMMG? So PETSc comes with a multigrid preconditioner and solver?</div>
<div> </div>
<div>Thank you<br><br> </div>
<div><span class="gmail_quote">On 1/26/07, <b class="gmail_sendername">Matthew Knepley</b> <<a href="mailto:knepley@gmail.com">knepley@gmail.com</a>> wrote:</span>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"><span class="q">On 1/25/07, <b class="gmail_sendername">Ben Tay</b> <<a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:zonexo@gmail.com" target="_blank">
zonexo@gmail.com</a>> wrote:</span>
<div><span class="q"><span class="gmail_quote"></span>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0pt 0pt 0pt 0.8ex; BORDER-LEFT: rgb(204,204,204) 1px solid">
<div>Hi,</div>
<div> </div>
<div>I was discussing with another user in another forum (<a onclick="return top.js.OpenExtLink(window,event,this)" href="http://cfd-online.com/" target="_blank">cfd-online.com</a>) about using PETSc in my cfd code. I am now using KSP to solve my momentum and poisson eqn by inserting values into the matrix. I was told that using PETSc this way is only for unstructured grids. It is very inefficient and much slower if I'm using it for my structured grid because I am not exploiting the regular structure of my grid.
</div>
<div> </div>
<div>Is that true? I'm solving flow around airfoil using c-grid.</div></blockquote></span>
<div><br>If you are using a Cartesian grid, the DA formulation is better. However, this nonsense from people about<br>"massive inefficiency" is just crap. There is a small difference in time which is almost trivial. However, there
<br>is a big difference in ease of programming. I am always fascinated how people can magnify small problems<br>in order to preserve their job. <br> </div><span class="q"><br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0pt 0pt 0pt 0.8ex; BORDER-LEFT: rgb(204,204,204) 1px solid">
<div>So how can I improve? Is it by using DA? I took a glance and it seems quite complicated.</div></blockquote></span>
<div><br>Wrong glance. Much simpler. <br> </div><span class="q"><br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0pt 0pt 0pt 0.8ex; BORDER-LEFT: rgb(204,204,204) 1px solid">
<div>Also, is multigrid available in PETSc? Chapter 7 discusses about it but it seems very brief. Is there a more elaborate tutorial besides that c examples?</div></blockquote></span>
<div><br>Yes, use DMMG. Much easier with DA.<br><br> Matt <br> </div><span class="q"><br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0pt 0pt 0pt 0.8ex; BORDER-LEFT: rgb(204,204,204) 1px solid">
<div>Hope someone can give me some ideas.</div>
<div> </div>
<div>Thank you.</div>
<div> </div>
<div> </div></blockquote></span></div><br><br clear="all"><br>-- <br>One trouble is that despite this system, anyone who reads journals widely<br>and critically is forced to realize that there are scarcely any bars to eventual
<br>publication. There seems to be no study too fragmented, no hypothesis too <br>trivial, no literature citation too biased or too egotistical, no design too<br>warped, no methodology too bungled, no presentation of results too
<br>inaccurate, too obscure, and too contradictory, no analysis too self-serving, <br>no argument too circular, no conclusions too trifling or too unjustified, and<br>no grammar and syntax too offensive for a paper to end up in print. -- Drummond Rennie
</blockquote></div><br>