BiCGStab memory footprint estimation

[tpadioleau]

Hi, I am using the BiCGStab algorithm, I was wondering if you could give an estimation of the maximum memory footprint needed by Ginkgo during the apply call ? In function of the parameters of the problem:

• the size of the matrix,
• the number of right-hand sides,
• no preconditioning,
• a convergence logger.

Thanks a lot,
Thomas

[pratikvn]

Does this comment block maybe help:

ginkgo/core/solver/bicgstab.cpp

Line 144 in ded657c

/* Memory movement summary:

?

[tpadioleau]

I think so but can you clarify the meaning of "values" ? Is it the number of rhs ?

[pratikvn]

Yes, I think so. values = nrhs * fp_bytes, where nrhs is the number of rhs and fp_bytes is the number of bytes used for the floating point calculations (except when accessor is used), 4 for float, and 8 for double.

The storage for the matrix will depend on the matrix format used.

[tpadioleau]

Thanks ok I understand. Is this * values missing for the rest of the operations ? The second line says

31n * values + 2 * matrix/preconditioner storage

I guess it is supposed to be the summation of all the operations mentioned below ?

[pratikvn]

Yes. It seems to be missing. 31n * values + ... is the summation of all the operations, so that is the one you need (and that should be correct). When not using a preconditioner, we just do a copy between vectors. So, you can replace the preconditioning operation (2n * values + storage) with a copy instead, which should be 2n * values.

[tpadioleau]

Thanks a lot