<div class="gmail_quote">Geometric multigrid needs more information than algebraic multigrid. It's a fact or life. In exchange, it can often be more efficient.</div><div class="gmail_quote"><br></div><div class="gmail_quote">
You likely notice that algebraic multigrid applied directly to the Stokes problem fails, so you need to do more anyway. If you are happy with the performance of using FieldSplit and applying BoomerAMG (or PCGAMG, or PCML) to the viscous (velocity-velocity) part, then use that. If you aren't happy with it, then try other methods, but some of those will need more information.</div>
<div class="gmail_quote"><br></div><div class="gmail_quote">On Thu, Feb 2, 2012 at 10:04, gouarin <span dir="ltr"><<a href="mailto:loic.gouarin@math.u-psud.fr">loic.gouarin@math.u-psud.fr</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">It is not hard to use multigrid on velocity if I provide the
interpolation as I said in my first email and as you say here. But
it is for me too intrusive because I have to do a special case to
use a multigrid pcmg whereas I can use boomeramg easily. I don't
know if what I say is clear ...<br>
<br>
The idea is to test many solvers on this problem.<br></div></blockquote></div><br>