[petsc-users] -log_view hangs unexpectedly // how to optimize my kspsolve
Matthew Knepley
knepley at gmail.com
Sat Jan 7 17:21:33 CST 2017
On Sat, Jan 7, 2017 at 4:59 PM, Manuel Valera <mvalera at mail.sdsu.edu> wrote:
> I would have to think and code a MWE for this problem before sending it
> since the model is much bigger than the petsc solver. Attached here is a
> screenshot of the debugger as barry taught me, is that the stack trace you
> need ?
>
> the ucmsMain.f90:522 that shows is the call (from all processes) to the
> routine that updates the rhs vector (from root) and scatters it (from all
> processes).
>
Yes, so one process is here and the other has moved on, so there is a
mismatch in calls.
You could do what Barry suggests, but I think it would be better to just
step through your main routine once (its slow going), and
see where the divergence happens.
Matt
> This routine is itself inside a double loop that occurs in all processes
> but the only call from all processes to the solver is this one, the rest of
> the loop which involves correcting for velocities, pressure and
> temperature, all happens in root node.
>
> Sorry for the convoluted program design, this is the first beta version of
> the model working on parallel and was the best i could come with, i suppose
> it makes more sense in serial,
>
> Thanks
>
> On Sat, Jan 7, 2017 at 2:24 PM, Matthew Knepley <knepley at gmail.com> wrote:
>
>> On Sat, Jan 7, 2017 at 4:20 PM, Manuel Valera <mvalera at mail.sdsu.edu>
>> wrote:
>>
>>> Thank you Matthew,
>>>
>>> On Sat, Jan 7, 2017 at 1:49 PM, Matthew Knepley <knepley at gmail.com>
>>> wrote:
>>>
>>>> On Sat, Jan 7, 2017 at 3:32 PM, Manuel Valera <mvalera at mail.sdsu.edu>
>>>> wrote:
>>>>
>>>>> Hi Devs, hope you are having a great weekend,
>>>>>
>>>>> I could finally parallelize my linear solver and implement it into the
>>>>> rest of the code in a way that only the linear system is solved in
>>>>> parallel, great news for my team, but there is a catch and is that i don't
>>>>> see any speedup in the linear system, i don't know if its the MPI in the
>>>>> cluster we are using, but im not sure on how to debug it,
>>>>>
>>>>
>>>> We need to see -log_view output for any performance question.
>>>>
>>>>
>>>>> On the other hand and because of this issue i was trying to do
>>>>> -log_summary or -log_view and i noticed the program in this context hangs
>>>>> when is time of producing the log, if i debug this for 2 cores, process 0
>>>>> exits normally but process 1 hangs in the vectorscatterbegin() with
>>>>> scatter_reverse way back in the code,
>>>>>
>>>>
>>>> You are calling a collective routine from only 1 process.
>>>>
>>>>
>>> Matt
>>>>
>>>
>>> I am pretty confident this is not the case,
>>>
>>
>> This is still the simplest explanation. Can you send the stack trace for
>> the 2 process run?
>>
>>
>>> the callings to vecscattercreatetozero and vecscatterbegin are made in
>>> all processes, the program goes thru all of the iterations on the linear
>>> solver, writes output correctly and even closes all the petsc objects
>>> without complaining, the freeze occurs at the very end when the log is to
>>> be produced.
>>>
>>
>> If you can send us a code to run, we can likely find the error.
>>
>> Thanks,
>>
>> Matt
>>
>>
>>> Thanks,
>>>
>>> Manuel
>>>
>>>
>>>
>>>>
>>>>
>>>>> and even after destroying all associated objects and calling
>>>>> petscfinalize(), so im really clueless on why is this, as it only happens
>>>>> for -log_* or -ksp_view options.
>>>>>
>>>>> my -ksp_view shows this:
>>>>>
>>>>> KSP Object: 2 MPI processes
>>>>>
>>>>> type: gcr
>>>>>
>>>>> GCR: restart = 30
>>>>>
>>>>> GCR: restarts performed = 20
>>>>>
>>>>> maximum iterations=10000, initial guess is zero
>>>>>
>>>>> tolerances: relative=1e-14, absolute=1e-50, divergence=10000.
>>>>>
>>>>> right preconditioning
>>>>>
>>>>> using UNPRECONDITIONED norm type for convergence test
>>>>>
>>>>> PC Object: 2 MPI processes
>>>>>
>>>>> type: bjacobi
>>>>>
>>>>> block Jacobi: number of blocks = 2
>>>>>
>>>>> Local solve is same for all blocks, in the following KSP and PC
>>>>> objects:
>>>>>
>>>>> KSP Object: (sub_) 1 MPI processes
>>>>>
>>>>> type: preonly
>>>>>
>>>>> maximum iterations=10000, initial guess is zero
>>>>>
>>>>> tolerances: relative=1e-05, absolute=1e-50, divergence=10000.
>>>>>
>>>>> left preconditioning
>>>>>
>>>>> using NONE norm type for convergence test
>>>>>
>>>>> PC Object: (sub_) 1 MPI processes
>>>>>
>>>>> type: ilu
>>>>>
>>>>> ILU: out-of-place factorization
>>>>>
>>>>> 0 levels of fill
>>>>>
>>>>> tolerance for zero pivot 2.22045e-14
>>>>>
>>>>> matrix ordering: natural
>>>>>
>>>>> factor fill ratio given 1., needed 1.
>>>>>
>>>>> Factored matrix follows:
>>>>>
>>>>> Mat Object: 1 MPI processes
>>>>>
>>>>> type: seqaij
>>>>>
>>>>> rows=100000, cols=100000
>>>>>
>>>>> package used to perform factorization: petsc
>>>>>
>>>>> total: nonzeros=1675180, allocated nonzeros=1675180
>>>>>
>>>>> total number of mallocs used during MatSetValues calls =0
>>>>>
>>>>> not using I-node routines
>>>>>
>>>>> linear system matrix = precond matrix:
>>>>>
>>>>> Mat Object: 1 MPI processes
>>>>>
>>>>> type: seqaij
>>>>>
>>>>> rows=100000, cols=100000
>>>>>
>>>>> total: nonzeros=1675180, allocated nonzeros=1675180
>>>>>
>>>>> total number of mallocs used during MatSetValues calls =0
>>>>>
>>>>> not using I-node routines
>>>>>
>>>>> linear system matrix = precond matrix:
>>>>>
>>>>> Mat Object: 2 MPI processes
>>>>>
>>>>> type: mpiaij
>>>>>
>>>>> rows=200000, cols=200000
>>>>>
>>>>> total: nonzeros=3373340, allocated nonzeros=3373340
>>>>>
>>>>> total number of mallocs used during MatSetValues calls =0
>>>>>
>>>>> not using I-node (on process 0) routines
>>>>>
>>>>>
>>>>>
>>>>> And i configured my PC object as:
>>>>>
>>>>>
>>>>> call PCSetType(mg,PCHYPRE,ierr)
>>>>>
>>>>> call PCHYPRESetType(mg,'boomeramg',ierr)
>>>>>
>>>>>
>>>>> call PetscOptionsSetValue(PETSC_NULL_OBJECT,'pc_hypre_boomeramg_n
>>>>> odal_coarsen','1',ierr)
>>>>>
>>>>> call PetscOptionsSetValue(PETSC_NULL_OBJECT,'pc_hypre_boomeramg_v
>>>>> ec_interp_variant','1',ierr)
>>>>>
>>>>>
>>>>>
>>>>> What are your thoughts ?
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Manuel
>>>>>
>>>>>
>>>>>
>>>>> On Fri, Jan 6, 2017 at 1:58 PM, Manuel Valera <mvalera at mail.sdsu.edu>
>>>>> wrote:
>>>>>
>>>>>> Awesome, that did it, thanks once again.
>>>>>>
>>>>>>
>>>>>> On Fri, Jan 6, 2017 at 1:53 PM, Barry Smith <bsmith at mcs.anl.gov>
>>>>>> wrote:
>>>>>>
>>>>>>>
>>>>>>> Take the scatter out of the if () since everyone does it and get
>>>>>>> rid of the VecView().
>>>>>>>
>>>>>>> Does this work? If not where is it hanging?
>>>>>>>
>>>>>>>
>>>>>>> > On Jan 6, 2017, at 3:29 PM, Manuel Valera <mvalera at mail.sdsu.edu>
>>>>>>> wrote:
>>>>>>> >
>>>>>>> > Thanks Dave,
>>>>>>> >
>>>>>>> > I think is interesting it never gave an error on this, after
>>>>>>> adding the vecassembly calls it still shows the same behavior, without
>>>>>>> complaining, i did:
>>>>>>> >
>>>>>>> > if(rankl==0)then
>>>>>>> >
>>>>>>> > call VecSetValues(bp0,nbdp,ind,Rhs,INSERT_VALUES,ierr)
>>>>>>> > call VecAssemblyBegin(bp0,ierr) ; call
>>>>>>> VecAssemblyEnd(bp0,ierr);
>>>>>>> > CHKERRQ(ierr)
>>>>>>> >
>>>>>>> endif
>>>>>>> >
>>>>>>> >
>>>>>>> > call VecScatterBegin(ctr,bp0,bp2,IN
>>>>>>> SERT_VALUES,SCATTER_REVERSE,ierr)
>>>>>>> > call VecScatterEnd(ctr,bp0,bp2,INSE
>>>>>>> RT_VALUES,SCATTER_REVERSE,ierr)
>>>>>>> > print*,"done! "
>>>>>>> > CHKERRQ(ierr)
>>>>>>> >
>>>>>>> >
>>>>>>> > CHKERRQ(ierr)
>>>>>>> >
>>>>>>> >
>>>>>>> > Thanks.
>>>>>>> >
>>>>>>> > On Fri, Jan 6, 2017 at 12:44 PM, Dave May <dave.mayhem23 at gmail.com>
>>>>>>> wrote:
>>>>>>> >
>>>>>>> >
>>>>>>> > On 6 January 2017 at 20:24, Manuel Valera <mvalera at mail.sdsu.edu>
>>>>>>> wrote:
>>>>>>> > Great help Barry, i totally had overlooked that option (it is
>>>>>>> explicit in the vecscatterbegin call help page but not in
>>>>>>> vecscattercreatetozero, as i read later)
>>>>>>> >
>>>>>>> > So i used that and it works partially, it scatters te values
>>>>>>> assigned in root but not the rest, if i call vecscatterbegin from outside
>>>>>>> root it hangs, the code currently look as this:
>>>>>>> >
>>>>>>> > call VecScatterCreateToZero(bp2,ctr,bp0,ierr); CHKERRQ(ierr)
>>>>>>> >
>>>>>>> > call PetscObjectSetName(bp0, 'bp0:',ierr)
>>>>>>> >
>>>>>>> > if(rankl==0)then
>>>>>>> >
>>>>>>> > call VecSetValues(bp0,nbdp,ind,Rhs,INSERT_VALUES,ierr)
>>>>>>> >
>>>>>>> > call VecView(bp0,PETSC_VIEWER_STDOUT_WORLD,ierr)
>>>>>>> >
>>>>>>> >
>>>>>>> > You need to call
>>>>>>> >
>>>>>>> > VecAssemblyBegin(bp0);
>>>>>>> > VecAssemblyEnd(bp0);
>>>>>>> > after your last call to VecSetValues() before you can do any
>>>>>>> operations with bp0.
>>>>>>> >
>>>>>>> > With your current code, the call to VecView should produce an
>>>>>>> error if you used the error checking macro CHKERRQ(ierr) (as should
>>>>>>> VecScatter{Begin,End}
>>>>>>> >
>>>>>>> > Thanks,
>>>>>>> > Dave
>>>>>>> >
>>>>>>> >
>>>>>>> > call VecScatterBegin(ctr,bp0,bp2,IN
>>>>>>> SERT_VALUES,SCATTER_REVERSE,ierr)
>>>>>>> > call VecScatterEnd(ctr,bp0,bp2,INSE
>>>>>>> RT_VALUES,SCATTER_REVERSE,ierr)
>>>>>>> > print*,"done! "
>>>>>>> > CHKERRQ(ierr)
>>>>>>> >
>>>>>>> > endif
>>>>>>> >
>>>>>>> > ! call VecScatterBegin(ctr,bp0,bp2,IN
>>>>>>> SERT_VALUES,SCATTER_REVERSE,ierr)
>>>>>>> > ! call VecScatterEnd(ctr,bp0,bp2,INSE
>>>>>>> RT_VALUES,SCATTER_REVERSE,ierr)
>>>>>>> >
>>>>>>> > call VecView(bp2,PETSC_VIEWER_STDOUT_WORLD,ierr)
>>>>>>> >
>>>>>>> > call PetscBarrier(PETSC_NULL_OBJECT,ierr)
>>>>>>> >
>>>>>>> > call exit()
>>>>>>> >
>>>>>>> >
>>>>>>> >
>>>>>>> > And the output is: (with bp the right answer)
>>>>>>> >
>>>>>>> > Vec Object:bp: 2 MPI processes
>>>>>>> > type: mpi
>>>>>>> > Process [0]
>>>>>>> > 1.
>>>>>>> > 2.
>>>>>>> > Process [1]
>>>>>>> > 4.
>>>>>>> > 3.
>>>>>>> > Vec Object:bp2: 2 MPI processes (before scatter)
>>>>>>> > type: mpi
>>>>>>> > Process [0]
>>>>>>> > 0.
>>>>>>> > 0.
>>>>>>> > Process [1]
>>>>>>> > 0.
>>>>>>> > 0.
>>>>>>> > Vec Object:bp0: 1 MPI processes
>>>>>>> > type: seq
>>>>>>> > 1.
>>>>>>> > 2.
>>>>>>> > 4.
>>>>>>> > 3.
>>>>>>> > done!
>>>>>>> > Vec Object:bp2: 2 MPI processes (after scatter)
>>>>>>> > type: mpi
>>>>>>> > Process [0]
>>>>>>> > 1.
>>>>>>> > 2.
>>>>>>> > Process [1]
>>>>>>> > 0.
>>>>>>> > 0.
>>>>>>> >
>>>>>>> >
>>>>>>> >
>>>>>>> >
>>>>>>> > Thanks inmensely for your help,
>>>>>>> >
>>>>>>> > Manuel
>>>>>>> >
>>>>>>> >
>>>>>>> > On Thu, Jan 5, 2017 at 4:39 PM, Barry Smith <bsmith at mcs.anl.gov>
>>>>>>> wrote:
>>>>>>> >
>>>>>>> > > On Jan 5, 2017, at 6:21 PM, Manuel Valera <mvalera at mail.sdsu.edu>
>>>>>>> wrote:
>>>>>>> > >
>>>>>>> > > Hello Devs is me again,
>>>>>>> > >
>>>>>>> > > I'm trying to distribute a vector to all called processes, the
>>>>>>> vector would be originally in root as a sequential vector and i would like
>>>>>>> to scatter it, what would the best call to do this ?
>>>>>>> > >
>>>>>>> > > I already know how to gather a distributed vector to root with
>>>>>>> VecScatterCreateToZero, this would be the inverse operation,
>>>>>>> >
>>>>>>> > Use the same VecScatter object but with SCATTER_REVERSE, not
>>>>>>> you need to reverse the two vector arguments as well.
>>>>>>> >
>>>>>>> >
>>>>>>> > > i'm currently trying with VecScatterCreate() and as of now im
>>>>>>> doing the following:
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > if(rank==0)then
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > call VecCreate(PETSC_COMM_SELF,bp0,ierr); CHKERRQ(ierr)
>>>>>>> !if i use WORLD
>>>>>>> > >
>>>>>>> !freezes in SetSizes
>>>>>>> > > call VecSetSizes(bp0,PETSC_DECIDE,nbdp,ierr); CHKERRQ(ierr)
>>>>>>> > > call VecSetType(bp0,VECSEQ,ierr)
>>>>>>> > > call VecSetFromOptions(bp0,ierr); CHKERRQ(ierr)
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > call VecSetValues(bp0,nbdp,ind,Rhs,INSERT_VALUES,ierr)
>>>>>>> > >
>>>>>>> > > !call VecSet(bp0,5.0D0,ierr); CHKERRQ(ierr)
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > call VecView(bp0,PETSC_VIEWER_STDOUT_WORLD,ierr)
>>>>>>> > >
>>>>>>> > > call VecAssemblyBegin(bp0,ierr) ; call
>>>>>>> VecAssemblyEnd(bp0,ierr) !rhs
>>>>>>> > >
>>>>>>> > > do i=0,nbdp-1,1
>>>>>>> > > ind(i+1) = i
>>>>>>> > > enddo
>>>>>>> > >
>>>>>>> > > call ISCreateGeneral(PETSC_COMM_SEL
>>>>>>> F,nbdp,ind,PETSC_COPY_VALUES,locis,ierr)
>>>>>>> > >
>>>>>>> > > !call VecScatterCreate(bp0,PETSC_NULL_OBJECT,bp2,is,ctr,ierr)
>>>>>>> !if i use SELF
>>>>>>> > >
>>>>>>> !freezes here.
>>>>>>> > >
>>>>>>> > > call VecScatterCreate(bp0,locis,bp2
>>>>>>> ,PETSC_NULL_OBJECT,ctr,ierr)
>>>>>>> > >
>>>>>>> > > endif
>>>>>>> > >
>>>>>>> > > bp2 being the receptor MPI vector to scatter to
>>>>>>> > >
>>>>>>> > > But it freezes in VecScatterCreate when trying to use more than
>>>>>>> one processor, what would be a better approach ?
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > Thanks once again,
>>>>>>> > >
>>>>>>> > > Manuel
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > On Wed, Jan 4, 2017 at 3:30 PM, Manuel Valera <
>>>>>>> mvalera at mail.sdsu.edu> wrote:
>>>>>>> > > Thanks i had no idea how to debug and read those logs, that
>>>>>>> solved this issue at least (i was sending a message from root to everyone
>>>>>>> else, but trying to catch from everyone else including root)
>>>>>>> > >
>>>>>>> > > Until next time, many thanks,
>>>>>>> > >
>>>>>>> > > Manuel
>>>>>>> > >
>>>>>>> > > On Wed, Jan 4, 2017 at 3:23 PM, Matthew Knepley <
>>>>>>> knepley at gmail.com> wrote:
>>>>>>> > > On Wed, Jan 4, 2017 at 5:21 PM, Manuel Valera <
>>>>>>> mvalera at mail.sdsu.edu> wrote:
>>>>>>> > > I did a PetscBarrier just before calling the vicariate routine
>>>>>>> and im pretty sure im calling it from every processor, code looks like this:
>>>>>>> > >
>>>>>>> > > From the gdb trace.
>>>>>>> > >
>>>>>>> > > Proc 0: Is in some MPI routine you call yourself, line 113
>>>>>>> > >
>>>>>>> > > Proc 1: Is in VecCreate(), line 130
>>>>>>> > >
>>>>>>> > > You need to fix your communication code.
>>>>>>> > >
>>>>>>> > > Matt
>>>>>>> > >
>>>>>>> > > call PetscBarrier(PETSC_NULL_OBJECT,ierr)
>>>>>>> > >
>>>>>>> > > print*,'entering POInit from',rank
>>>>>>> > > !call exit()
>>>>>>> > >
>>>>>>> > > call PetscObjsInit()
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > And output gives:
>>>>>>> > >
>>>>>>> > > entering POInit from 0
>>>>>>> > > entering POInit from 1
>>>>>>> > > entering POInit from 2
>>>>>>> > > entering POInit from 3
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > Still hangs in the same way,
>>>>>>> > >
>>>>>>> > > Thanks,
>>>>>>> > >
>>>>>>> > > Manuel
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > On Wed, Jan 4, 2017 at 2:55 PM, Manuel Valera <
>>>>>>> mvalera at mail.sdsu.edu> wrote:
>>>>>>> > > Thanks for the answers !
>>>>>>> > >
>>>>>>> > > heres the screenshot of what i got from bt in gdb (great hint in
>>>>>>> how to debug in petsc, didn't know that)
>>>>>>> > >
>>>>>>> > > I don't really know what to look at here,
>>>>>>> > >
>>>>>>> > > Thanks,
>>>>>>> > >
>>>>>>> > > Manuel
>>>>>>> > >
>>>>>>> > > On Wed, Jan 4, 2017 at 2:39 PM, Dave May <
>>>>>>> dave.mayhem23 at gmail.com> wrote:
>>>>>>> > > Are you certain ALL ranks in PETSC_COMM_WORLD call these
>>>>>>> function(s). These functions cannot be inside if statements like
>>>>>>> > > if (rank == 0){
>>>>>>> > > VecCreateMPI(...)
>>>>>>> > > }
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > On Wed, 4 Jan 2017 at 23:34, Manuel Valera <
>>>>>>> mvalera at mail.sdsu.edu> wrote:
>>>>>>> > > Thanks Dave for the quick answer, appreciate it,
>>>>>>> > >
>>>>>>> > > I just tried that and it didn't make a difference, any other
>>>>>>> suggestions ?
>>>>>>> > >
>>>>>>> > > Thanks,
>>>>>>> > > Manuel
>>>>>>> > >
>>>>>>> > > On Wed, Jan 4, 2017 at 2:29 PM, Dave May <
>>>>>>> dave.mayhem23 at gmail.com> wrote:
>>>>>>> > > You need to swap the order of your function calls.
>>>>>>> > > Call VecSetSizes() before VecSetType()
>>>>>>> > >
>>>>>>> > > Thanks,
>>>>>>> > > Dave
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > On Wed, 4 Jan 2017 at 23:21, Manuel Valera <
>>>>>>> mvalera at mail.sdsu.edu> wrote:
>>>>>>> > > Hello all, happy new year,
>>>>>>> > >
>>>>>>> > > I'm working on parallelizing my code, it worked and provided
>>>>>>> some results when i just called more than one processor, but created
>>>>>>> artifacts because i didn't need one image of the whole program in each
>>>>>>> processor, conflicting with each other.
>>>>>>> > >
>>>>>>> > > Since the pressure solver is the main part i need in parallel im
>>>>>>> chosing mpi to run everything in root processor until its time to solve for
>>>>>>> pressure, at this point im trying to create a distributed vector using
>>>>>>> either
>>>>>>> > >
>>>>>>> > > call VecCreateMPI(PETSC_COMM_WORLD,
>>>>>>> PETSC_DECIDE,nbdp,xp,ierr)
>>>>>>> > > or
>>>>>>> > > call VecCreate(PETSC_COMM_WORLD,xp,ierr); CHKERRQ(ierr)
>>>>>>> > > call VecSetType(xp,VECMPI,ierr)
>>>>>>> > > call VecSetSizes(xp,PETSC_DECIDE,nbdp,ierr); CHKERRQ(ierr)
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > In both cases program hangs at this point, something it never
>>>>>>> happened on the naive way i described before. I've made sure the global
>>>>>>> size, nbdp, is the same in every processor. What can be wrong?
>>>>>>> > >
>>>>>>> > > Thanks for your kind help,
>>>>>>> > >
>>>>>>> > > Manuel.
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > >
>>>>>>> > > --
>>>>>>> > > What most experimenters take for granted before they begin their
>>>>>>> experiments is infinitely more interesting than any results to which their
>>>>>>> experiments lead.
>>>>>>> > > -- Norbert Wiener
>>>>>>> > >
>>>>>>> > >
>>>>>>> >
>>>>>>> >
>>>>>>> >
>>>>>>> >
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> What most experimenters take for granted before they begin their
>>>> experiments is infinitely more interesting than any results to which their
>>>> experiments lead.
>>>> -- Norbert Wiener
>>>>
>>>
>>>
>>
>>
>> --
>> What most experimenters take for granted before they begin their
>> experiments is infinitely more interesting than any results to which their
>> experiments lead.
>> -- Norbert Wiener
>>
>
>
--
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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