<div dir="ltr"><div><div>To see all the fieldsplit options, run with<br></div>./ex70 -pc_type fieldsplit -help<br><br></div>-help will only display the options relevant to the current configuration of your KSP and PC.<br></div>
<div class="gmail_extra"><br><br><div class="gmail_quote">On 17 July 2014 00:10, Dave May <span dir="ltr"><<a href="mailto:dave.mayhem23@gmail.com" target="_blank">dave.mayhem23@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 dir="ltr"><div>Run with <br></div>-help<br></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><br><div class="gmail_quote">On 17 July 2014 00:07, Sun, Hui <span dir="ltr"><<a href="mailto:hus003@ucsd.edu" target="_blank">hus003@ucsd.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div style="direction:ltr;font-family:Tahoma;color:#000000;font-size:10pt">Thank you Dave, it does sol<font>ve the problem. Another question is: since some options like</font>
<div><font><font face="Times New Roman"><br>
</font></font></div>
<div><font><font face="Times New Roman">-</font></font><font style="font-size:small" face="Times New Roman">fieldsplit_0_pc_type</font><span style="font-size:small"> </span></div>
<div><span style="font-size:small"><br>
</span></div>
<div><span style="font-size:small">does not show up if I type</span></div>
<div><font style="font-size:small" face="Times New Roman"><br>
</font></div>
<div><span style="font-size:small"></span><font style="font-size:small" face="Times New Roman">./ex70 -help</font></div>
<div><span style="font-size:small"><br>
</span></div>
<div><span style="font-size:small">how then can I have a complete list of all the options? </span></div>
<div>
<div><br>
</div>
<div>Best,</div>
<div>Hui</div>
<div><br>
</div>
<div><br>
<div style="font-family:Times New Roman;color:#000000;font-size:16px">
<hr>
<div style="direction:ltr"><font color="#000000" face="Tahoma"><b>From:</b> Dave May [<a href="mailto:dave.mayhem23@gmail.com" target="_blank">dave.mayhem23@gmail.com</a>]<br>
<b>Sent:</b> Wednesday, July 16, 2014 2:57 PM<br>
<b>To:</b> Sun, Hui<br>
<b>Cc:</b> Matthew Knepley; <a href="mailto:petsc-users@mcs.anl.gov" target="_blank">petsc-users@mcs.anl.gov</a><div><div><br>
<b>Subject:</b> Re: [petsc-users] why a certain option cannot be used<br>
</div></div></font><br>
</div><div><div>
<div></div>
<div>You need to specify on the command line
<div>-pc_type fieldsplit -fieldsplit_0_pc_type xxx -fieldsplit_1_pc_type yyy</div>
<div><br>
</div>
<div>Where xxx and yyy are the desired preconditioners for the (1,1) block and (2,2) block. Note that the default PC (ilu(0)) applied to both splits will fail for this example.</div>
<div><br>
</div>
<div>The comments in the code are misleading and incorrect. Without the option <font><span>-pc_type fieldsplit, all fieldsplit options have no effect.</span></font></div>
<div><font><span><br>
</span></font></div>
<div><font><span></span><span>When debugging solvers, always run with - ksp_view (as Matt recommends) </span></font></div>
<div><font><span><br>
</span></font></div>
<div><font><span><br>
</span></font><br>
On Wednesday, 16 July 2014, Sun, Hui <<a href="mailto:hus003@ucsd.edu" target="_blank">hus003@ucsd.edu</a>> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div style="direction:ltr;font-family:Tahoma;color:#000000;font-size:10pt">No I don't think I'm using fieldsplitting although I want to use it. The output of
<div><span style="font-family:Menlo;font-size:11px"><br>
</span></div>
<div><span style="font-family:Menlo;font-size:11px">./ex70 -nx 32 -ny 48 -fieldsplit_1_pc_type jacobi -ksp_view</span></div>
<div><br>
</div>
<div>is the following: <span style="font-family:'Segoe UI',Helvetica,Arial,sans-serif;font-size:medium"> </span>
<div><br>
</div>
<div>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">KSP Object: 1 MPI processes</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> type: gmres</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> GMRES: restart=30, using Classical (unmodified) Gram-Schmidt Orthogonalization with no iterative refinement</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> GMRES: happy breakdown tolerance 1e-30</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> maximum iterations=10000, initial guess is zero</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> tolerances: relative=1e-05, absolute=1e-50, divergence=10000</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> left preconditioning</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> using PRECONDITIONED norm type for convergence test</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">PC Object: 1 MPI processes</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> type: none</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> linear system matrix = precond matrix:</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> Matrix Object: 1 MPI processes</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> type: nest</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> rows=4608, cols=4608</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> Matrix object: </p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> type=nest, rows=2, cols=2 </p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> MatNest structure: </p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> (0,0) : prefix="a00_", type=mpiaij, rows=3072, cols=3072 </p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> (0,1) : prefix="a01_", type=mpiaij, rows=3072, cols=1536 </p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> (1,0) : prefix="a10_", type=mpiaij, rows=1536, cols=3072 </p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> (1,1) : prefix="a11_", type=mpiaij, rows=1536, cols=1536 </p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> residual u = 2.6315e-05</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> residual p = 0.000229872</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> residual [u,p] = 0.000231373</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> discretization error u = 0.00633503</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> discretization error p = 0.121534</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> discretization error [u,p] = 0.121699</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">WARNING! There are options you set that were not used!</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">WARNING! could be spelling mistake, etc!</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">Option left: name:-fieldsplit_1_pc_type value: jacobi</p>
<div><br>
</div>
<div><br>
<div style="font-family:Times New Roman;color:#000000;font-size:16px">
<hr>
<div style="direction:ltr"><font color="#000000" face="Tahoma"><b>From:</b> Sun, Hui<br>
<b>Sent:</b> Wednesday, July 16, 2014 2:40 PM<br>
<b>To:</b> Matthew Knepley<br>
<b>Cc:</b> <a href="http://UrlBlockedError.aspx" target="_blank">petsc-users@mcs.anl.gov</a><br>
<b>Subject:</b> RE: [petsc-users] why a certain option cannot be used<br>
</font><br>
</div>
<div></div>
<div>
<div style="direction:ltr;font-family:Tahoma;color:#000000;font-size:10pt">Thank you Matt. I've corrected it to
<div><br>
</div>
<div>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">./ex70 -nx 32 -ny 48 -fieldsplit_1_pc_type jacobi</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><br>
</p>
<p style="margin-right:0px;margin-left:0px">However the output is still:</p>
<p style="margin-right:0px;margin-left:0px"><br>
</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">residual u = 2.6315e-05</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> residual p = 0.000229872</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> residual [u,p] = 0.000231373</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> discretization error u = 0.00633503</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> discretization error p = 0.121534</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> discretization error [u,p] = 0.121699</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">WARNING! There are options you set that were not used!</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">WARNING! could be spelling mistake, etc!</p>
<p style="margin-right:0px;margin-left:0px"></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">Option left: name:-fieldsplit_1_pc_type value: jacobi</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><br>
</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px">If I type</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px"><br>
</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">./ex70 -help | grep fieldsplit_1_</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px"><br>
</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px">the output is that nothing coming out. </span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px"><br>
</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px"><br>
</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><br>
</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><br>
</p>
<div style="font-family:Times New Roman;color:#000000;font-size:16px">
<hr>
<div style="direction:ltr"><font color="#000000" face="Tahoma"><b>From:</b> Matthew Knepley [<a href="http://UrlBlockedError.aspx" target="_blank">knepley@gmail.com</a>]<br>
<b>Sent:</b> Wednesday, July 16, 2014 2:32 PM<br>
<b>To:</b> Sun, Hui<br>
<b>Cc:</b> <a href="http://UrlBlockedError.aspx" target="_blank">petsc-users@mcs.anl.gov</a><br>
<b>Subject:</b> Re: [petsc-users] why a certain option cannot be used<br>
</font><br>
</div>
<div></div>
<div>
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">On Wed, Jul 16, 2014 at 4:25 PM, Matthew Knepley <span dir="ltr">
<<a href="http://UrlBlockedError.aspx" target="_blank">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 dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">
<div>On Wed, Jul 16, 2014 at 4:22 PM, Sun, Hui <span dir="ltr"><<a href="http://UrlBlockedError.aspx" target="_blank">hus003@ucsd.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div style="direction:ltr;font-family:Tahoma;color:#000000;font-size:10pt">Thank you Matt for answering, however even with that I don't think it works. For example, the command
<div><br>
</div>
<div>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">./ex70 -nx 32 -ny 48 -fieldsplit_1_type jacobi</p>
</div>
</div>
</div>
</blockquote>
<div><br>
</div>
</div>
<div>You have mistyped. Look carefully at my last message:</div>
<div><br>
</div>
<div> -fieldsplit_1_pc_type jacobi</div>
</div>
</div>
</div>
</blockquote>
<div><br>
</div>
<div>I also want to note that you can see all the available options with -help. It does produce</div>
<div>a lot of output, but you can segregate it by prefix ("fieldsplit_1_"). You can also see the</div>
<div>prefix of each solver component using -ksp_view.</div>
<div><br>
</div>
<div> Matt</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">
<div> Matt</div>
<div>
<div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div style="direction:ltr;font-family:Tahoma;color:#000000;font-size:10pt">
<div>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px">gives me the following output</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px"><br>
</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">residual u = 2.6315e-05</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> residual p = 0.000229872</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> residual [u,p] = 0.000231373</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> discretization error u = 0.00633503</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> discretization error p = 0.121534</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> discretization error [u,p] = 0.121699</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">WARNING! There are options you set that were not used!</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">WARNING! could be spelling mistake, etc!</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">Option left: name:-fieldsplit_1_type value: jacobi</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><br>
</p>
<p style="margin-right:0px;margin-left:0px">Furthermore, if I look into the possible options with keyword fieldsplit involved by the command:</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><br>
</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">./ex70 -help | grep -A5 fieldsplit</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px"><br>
</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px">I get this output:</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px"><br>
</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">eisenstat ilu icc cholesky asm gasm ksp composite redundant nn mat fieldsplit galerkin exotic hmpi asa cp lsc redistribute svd gamg tfs (PCSetType)</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> -pc_use_amat: <FALSE> use Amat (instead of Pmat) to define preconditioner in nested inner solves (PCSetUseAmat)</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">Krylov Method (KSP) options -------------------------------------------------</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> -ksp_type <gmres>: Krylov method (one of) cg groppcg pipecg cgne nash stcg gltr richardson</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> chebyshev gmres tcqmr bcgs ibcgs fbcgs fbcgsr bcgsl cgs tfqmr cr pipecr lsqr preonly qcg bicg fgmres minres symmlq lgmres lcd gcr pgmres specest dgmres (KSPSetType)</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> -ksp_max_it <10000>: Maximum number of iterations (KSPSetTolerances)</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><br>
</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px">So I don't see any option that's similar to -fieldsplit_1_type. </span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px"><br>
</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px">Hui</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><span style="font-family:Tahoma;font-size:13px"><br>
</span></p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"><br>
</p>
<div style="font-family:Times New Roman;color:#000000;font-size:16px">
<hr>
<div style="direction:ltr"><font color="#000000" face="Tahoma"><b>From:</b> Matthew Knepley [<a href="http://UrlBlockedError.aspx" target="_blank">knepley@gmail.com</a>]<br>
<b>Sent:</b> Wednesday, July 16, 2014 2:16 PM<br>
<b>To:</b> Sun, Hui<br>
<b>Cc:</b> <a href="http://UrlBlockedError.aspx" target="_blank">petsc-users@mcs.anl.gov</a><br>
<b>Subject:</b> Re: [petsc-users] why a certain option cannot be used<br>
</font><br>
</div>
<div></div>
<div>
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">On Wed, Jul 16, 2014 at 4:09 PM, Sun, Hui <span dir="ltr">
<<a href="http://UrlBlockedError.aspx" target="_blank">hus003@ucsd.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div style="direction:ltr;font-family:Tahoma;color:#000000;font-size:10pt">I want to solve Stokes equation using user defined schur complement preconditioner. So I'm reading and testing snes/examples/tutorial/ex55.c, and ex70.c. In these examples, there
are comments about the usage, for example:
<div><span style="color:rgb(215,57,30);font-family:Menlo;font-size:11px"><br>
</span></div>
<div><span style="color:rgb(215,57,30);font-family:Menlo;font-size:11px">mpiexec -n 2 ./stokes -nx 32 -ny 48 -fieldsplit_1_user_pc. </span>
<div><span style="font-size:10pt"><br>
</span></div>
<div><span style="font-size:10pt">However the option </span><span style="color:rgb(215,57,30);font-family:Menlo;font-size:11px">-fieldsplit_1_user_pc</span><span style="font-size:10pt"> is not recognized by the executable. The output of the above command
is:</span></div>
</div>
</div>
</div>
</blockquote>
<div><br>
</div>
<div>This ("user_pc") is just a mnemonic. What it means is that you can use any PC in this slot. What he should have written is</div>
<div><br>
</div>
<div> -fieldsplit_1_pc_type <user pc></div>
<div><br>
</div>
<div> Thanks,</div>
<div><br>
</div>
<div> Matt</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div style="direction:ltr;font-family:Tahoma;color:#000000;font-size:10pt">
<div>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> residual u = 2.6315e-05</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> residual p = 0.000229872</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> residual [u,p] = 0.000231373</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> discretization error u = 0.00633503</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> discretization error p = 0.121534</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo"> discretization error [u,p] = 0.121699</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">WARNING! There are options you set that were not used!</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">WARNING! could be spelling mistake, etc!</p>
<p style="margin-right:0px;margin-left:0px;font-size:11px;font-family:Menlo">Option left: name:-fieldsplit_1_user_pc (no value)</p>
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<p style="margin-right:0px;margin-left:0px">I'm wondering what's going on. Is that because I need some specific options during my configuring of the package? By the way, the version of PETSc I'm using is 3.4.4. </p>
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<p style="margin-right:0px;margin-left:0px">Best,</p>
<p style="margin-right:0px;margin-left:0px">Hui</p>
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What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>
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