<div class="gmail_quote">On Fri, Feb 17, 2012 at 06:54, Thomas Witkowski <span dir="ltr"><<a href="mailto:thomas.witkowski@tu-dresden.de">thomas.witkowski@tu-dresden.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Maybe some related question: Most textbooks write that the compatibility condition to solve a system with constant null space is that the right hand side has zero mean value. Today I read part of the Multigrid-book written by Trottenberg, and there the condition is written in a different form (eq 5.6.22 on page 185): the integral of the right hand side must be equal on the whole domain and on the boundary. Does any of you have an explanation for this condition? Is there a book/paper that considers the compatibility condition in more details?</blockquote>
</div><br><div>It's common to project the null space out of the right hand side (yielding a "consistent" right hand side).</div>