On 1/25/07, <b class="gmail_sendername">Ben Tay</b> <<a href="mailto:zonexo@gmail.com">zonexo@gmail.com</a>> wrote:<div><span class="gmail_quote"></span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div>Hi,</div>
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<div>I was discussing with another user in another forum (<a href="http://cfd-online.com" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">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.
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<div>Is that true? I'm solving flow around airfoil using c-grid.</div></blockquote><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><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div>So how can I improve? Is it by using DA? I took a glance and it seems quite complicated.</div></blockquote><div><br>Wrong glance. Much simpler. <br></div><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<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><div><br>Yes, use DMMG. Much easier with DA.<br>
<br> Matt <br></div><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div>Hope someone can give me some ideas.</div>
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<div>Thank you.</div>
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</blockquote></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