<div class="gmail_quote">On Wed, Jan 4, 2012 at 10:40, Matthew Knepley <span dir="ltr"><<a href="mailto:knepley@gmail.com">knepley@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><div class="im"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">I have just noticed that MatGetRowMinAbs (but not the Max variant) in<br>
some cases returns a very small negative number like -1.62505e-17<br>
(displayed as %g). Is this an epsilon effect or an indication of a<br>
problem?<br></blockquote><div><br></div></div></div><div>Its not possible that was actually the minimum element?</div></blockquote></div><br><div>It is supposed to be returning the absolute value anyway, so no. Also, due to this patch of yours</div>
<div><br></div><div><a href="http://petsc.cs.iit.edu/petsc/petsc-dev/rev/e433a0">http://petsc.cs.iit.edu/petsc/petsc-dev/rev/e433a0</a></div><div><br></div><div>it should never return a value smaller than 1e-12 that isn't identically zero. I don't understand why this shift is being done, but I think that if you want a shift like this, it should at least be relative to the norm of the vector or something.</div>