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<div style="font-size: 10pt;"><div dir="ltr" style="margin-top:0;margin-bottom:0;">Hello Florian,</div><div dir="ltr" style="margin-top:0;margin-bottom:0;"><br></div><div dir="ltr" style="margin-top:0;margin-bottom:0;">I usually apply following steps before going to preconditioners;</div><div dir="ltr" style="margin-top:0;margin-bottom:0;"><br></div><div dir="ltr" style="margin-top:0;margin-bottom:0;">- Construct a smaller matrix and examine the nonzeros, try to use permutations to get a smaller bandwidth (minimum degree or symrcm).</div><div dir="ltr" style="margin-top:0;margin-bottom:0;"><br></div><div dir="ltr" style="margin-top:0;margin-bottom:0;">- Use symmetric diagonal scaling, which usually helps a lot but mostly not enough by itself.</div><div dir="ltr" style="margin-top:0;margin-bottom:0;"><br></div><div dir="ltr" style="margin-top:0;margin-bottom:0;">- I have found out that (as a part of my master thesis), ParaSails is a good general purpose preconditioner and
you can have symmetric ParaSails preconditioners easily.</div><div dir="ltr" style="margin-top:0;margin-bottom:0;"><br></div><div dir="ltr" style="margin-top:0;margin-bottom:0;">I hope this helps. </div><div dir="ltr" style="margin-top:0;margin-bottom:0;"><br></div><div dir="ltr" style="margin-top:0;margin-bottom:0;">Regards,</div><div dir="ltr" style="margin-top:0;margin-bottom:0;">Abdullah Ali Sivas</div></div>
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