[petsc-users] slepc eating all my ram

[Hong]

Simon :
For '-eps_hermitian -eps_largest_magnitude', why do you need 'spectral
transform'?
Try slepc default method for ex3.c.

Hong

>
> Hi,
>
> I'm running a slepc eigenvalue solver on a single machine with 198GB of
> ram,
> and solution space dimension 2^32. With double precision this means
> each vector is 32GB. I'm using shell matrices to implement the matrix
> vector product. I figured the easiest way to get eigenvalues is using
> the slepc power method, but it is still eating all the ram.
>
> Running in gdb I see that slepc is allocating a bunch of vectors in
> the spectral transform object (in STSetUp), and by this time it has
> consumed
> most of the 198GB of ram. I don't see why a spectral transform
> shift of zero needs to alloc a whole bunch of memory.
>
> I'm wondering if there are some other options to slepc that can
> reduce the memory footprint? A barebones implementation of the
> power method only needs to keep two vectors, perhaps I should
> just try doing this using petsc primitives. It's also possible that
> I could spread the computation over two or more machines but
> that's a whole other learning curve.
>
> The code I am running is essentially the laplacian grid
> example from slepc (src/eps/examples/tutorials/ex3.c):
>
> ./ex3 -eps_hermitian -eps_largest_magnitude -eps_monitor ascii -eps_nev 1
> -eps_type power -n 65536
>
> I also put this line in the source:
> EPSSetDimensions(eps,1,2,1);
>
> Cheers,
>
> Simon.
>
>
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