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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Matt,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Thanks for replying back to me. Actually, we are only seeing this problem on debug, non-fortran compilations of PETSc. When we turn on fortran and turn off
debugging in the configuration, the behavior is normal, the timing is fast (as to be expected), and the storage space is more in lines with our calculations. Maybe this is expected behavior for all debug/non-fortran builds? Or maybe this is a test case for
finding an edge-case?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Anyways, thanks for your help!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">-Brenna<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> petsc-users-bounces@mcs.anl.gov [mailto:petsc-users-bounces@mcs.anl.gov]
<b>On Behalf Of </b>Matthew Knepley<br>
<b>Sent:</b> Thursday, May 17, 2012 10:59 AM<br>
<b>To:</b> PETSc users list<br>
<b>Subject:</b> [EXTERNAL] Re: [petsc-users] Problem creating an array of KSP objects<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">On Thu, May 17, 2012 at 12:37 PM, Hautzenroeder, Brenna M <<a href="mailto:bmhautz@sandia.gov" target="_blank">bmhautz@sandia.gov</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">I’m running into time and memory problems creating an array to store multiple KSP objects.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">We are using a Fourier method for the temporal portion of our operator; currently, this is anywhere between 1024-2048 time samples equating to 1024-2048 frequencies to advance
our solution. Each frequency has its own matrix, meaning there are 1024-2048 linear equations of the form Ax = b. So, while the matrices are different for each frequency, when we propagate the solution one step, the 1024-2048 matrices don’t change since the
frequencies haven’t changed between steps.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">We would like to store each KSP solution (all 1024-2048 of them) in an array so that we can reuse them for the next step since this saves us time factoring the matrix. The
problem I am seeing is that storing these KSP objects in any kind of array increases the runtime and storage space exponentially – I am seeing times on the order of 30 mins to an hour and memory consumed hover around 20-30GB! Is there something inherent
<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I don't think you really mean "exponential", but just big. Did you calculate how much space you expect? Storing a factor can take<o:p></o:p></p>
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<p class="MsoNormal">N^3 space, and then you have 1000 of them, so it will take 1000x the space of 1 KSP. Did you compare the storage for both cases?<o:p></o:p></p>
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<p class="MsoNormal">There is really not enough information in your question, however<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> Yes, storing KSPs is the right thing here<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> No, they do not take more space than necessary<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> Matt<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">about the KSP object that I am missing and/or a better way to store these objects? I don’t have any problems if I use one KSP object and set the operators each time to the
different matrices, except that it takes longer than it normally would after the first step since it has to recalculate the preconditioner matrix.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Note: We are using distributed matrices and vectors for our linear system.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">I have included some pseudocode to illustrate our linear system, which works:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">KSP k;<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">for steps = 1 to 100 do:<o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:.5in"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">for time = 1 to 1024 do:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> create distributed matrix A and fill with local values (A[step=1,time=1] = A[step=2,time=1], etc)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> create distributed vector b and fill with local values for given time<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> create distributed vector x for result<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> create KSP k and set matrices<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> KSPSolve(k, b, x) => takes a little extra time each step<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">However, the following creates time/storage problems:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">KSP* kArray;<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">create kArray => takes inordinate amout of time and storage<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">for steps = 1 to 100 do:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> for time=1 to 1024 do:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> create distributed matrix A and fill with local values (A[step=1,time=1] = A[step=2,time=1], etc)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> create distributed vector b and fill with local values for given time<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> create distributed vector x for result<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> if time == 1 do:<o:p></o:p></span></p>
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<p class="MsoNormal" style="text-indent:.5in"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">set matrices on kArray[time] => also takes an inordinate amount of time and storage<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> KSPSolve(kArray[time], b, x)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Any insight would be greatly appreciated!<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#888888">Brenna<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#888888"> <o:p></o:p></span></p>
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<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-- <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<o:p></o:p></p>
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