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<div class="moz-cite-prefix">On 09/08/2013 03:38 PM, Dave May wrote:<br>
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<div>Remove the option<br>
-fieldsplit_1_pc_type icc<br>
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It is clobbering the LU option Matt suggested you try first (
-fieldsplit_1_pc_type lu)<br>
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Dear Dave,<br>
<br>
I also realized this but and changed that with <br>
<br>
-fieldsplit_2_pc_type icc<br>
<br>
but thanks for looking at that, need a break I guess ;-)<br>
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When debigging such solvers, you should always run with
-ksp_view to check your solver is configured correctly.<br>
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Thanks for this<br>
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On 8 September 2013 15:32, Umut Tabak <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:u.tabak@tudelft.nl"
target="_blank">u.tabak@tudelft.nl</a>></span> wrote:<br>
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<div>On 09/08/2013 03:00 PM, Matthew Knepley wrote:<br>
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<div>If you want to solve hard systems, you must
learn to debug a solver yourself. What does
"just hangs" mean? Start with a full</div>
<div>Schur complement factorization with LU on
block 1 and a tiny tolerance on block 2. This
will converge in 1 iterate. Then</div>
<div>start slowly making the preconditioner
weaker.</div>
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Hi Matt,<br>
<br>
Thanks for the suggestion but I did not completely
understand the options to use for this, I am still
learning the fieldsplit interface. It was my mistake to
not to give more in formation on what 'Just hangs' means,
sorry.<br>
<br>
For the previous message: that meant extremely slow
iterations, the iteration process was not advancing at
all.<br>
<br>
After your reply and looking at the fieldsplit options a
bit more, I came up with these set of options, now
iterations are going fast but the decrease in relative
residual is so slow. But apparently this does not converge
in 1 iteration, I am still mistaken at some point.<br>
<br>
./ex3 -pc_type fieldsplit -pc_fieldsplit_type schur
-fieldsplit_1_pc_type lu -fieldsplit_1_ksp_type preonly
-fieldsplit_1_pc_type icc -fieldsplit_2_ksp_type minres
-fieldsplit_2_ksp_rtol 1e-8
-pc_fieldsplit_schur_factorization_type full
-ksp_monitor_true_residual<br>
<br>
Maybe you can help me at this point again.<br>
<br>
Thanks.<span class="HOEnZb"><font color="#888888"><br>
Umut</font></span>
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<div> Matt</div>
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<blockquote class="gmail_quote"
style="margin:0 0 0 .8ex;border-left:1px
#ccc solid;padding-left:1ex"> The system is
a symmetric system in this case given as<br>
<br>
A =<br>
A11 C<br>
C^T A22<br>
<br>
C is of size 1490X2432<br>
<br>
Could you please comment on this point for
me, do I still have an error on the problem
setup or on the usage of the options?<br>
<br>
BR,<br>
Umut
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style="margin:0 0 0
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solid;padding-left:1ex"> <br>
ISCreateBlock(PETSC_COMM_SELF,bs,n1,inputindices,PETSC_COPY_VALUES,&is_row1);<br>
ISCreateBlock(PETSC_COMM_SELF,bs,n2,inputindices,PETSC_COPY_VALUES,&is_row2);<br>
<br>
We could check for this case, but it
would require a little code and<br>
isn't currently done. This is
probably what you wanted:<br>
<br>
diff --git i/ex2.c w/ex2.c<br>
index 94cea2c..0cce3e6 100644<br>
--- i/ex2.c<br>
+++ w/ex2.c<br>
@@ -45,7 +45,7 @@ int main(int
argc,char **args)<br>
PetscInt bs = 2, n1=1, n2=1,
inputindices[]={0,1}; /* block size is
2 */<br>
ISCreateBlock(PETSC_COMM_SELF,bs,n1,inputindices,PETSC_COPY_VALUES,&is_row1);<br>
-
ISCreateBlock(PETSC_COMM_SELF,bs,n2,inputindices,PETSC_COPY_VALUES,&is_row2);<br>
+
ISCreateBlock(PETSC_COMM_SELF,bs,n2,inputindices+n1,PETSC_COPY_VALUES,&is_row2);<br>
ISView(is_row1,PETSC_VIEWER_STDOUT_SELF);<br>
ISView(is_row2,PETSC_VIEWER_STDOUT_SELF);<br>
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-- <br>
What most experimenters take for granted before
they begin their experiments is infinitely more
interesting than any results to which their
experiments lead.<br>
-- Norbert Wiener </div>
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