<p>Yes, this usually works as long as the preconditioner for A is stable on the non-null subspace.</p>
<div class="gmail_quote">On Jan 9, 2012 5:43 PM, "Geoffrey Irving" <<a href="mailto:irving@naml.us">irving@naml.us</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hello,<br>
<br>
I have a matrix A and an orthogonal projection operator P onto a<br>
fairly large (but sparse) linear subspace. I want to solve the system<br>
<br>
PAPx = Pb<br>
<br>
If set up a MatNullSpace object with MatNullSpaceSetFunction, with KSP<br>
solve the system I want even if A is nonsingular?<br>
<br>
Thanks,<br>
Geoffrey<br>
</blockquote></div>