IFCHAR = T ??

[fischer1]

I notice that several examples have ifchar=T.

Some don't even use a dt big enough to warrant such usage (e.g., cyl_restart case).

I think all examples (except for short tests designed to test Characteristics) should have IFCHAR F unless we really want to show off CFL >> 1.

Otherwise, jobs will run twice as slow. People often start with one of the examples and modify it to suit their needs without realizing that IFCHAR=T.

(This happened in one of the large KTH runs that George did for pipe flow. He was running with CFL=0.5 and IFCHAR T. Turning that to F sped the code up by 2X and would have saved a million core hours---it was my fault for not paying attention earlier that time.)

Can we / should we switch all the examples to have default IFCHAR F (since the decision
to use Characteristics is typically a more advanced-user decision) ?

[stgeke]

I agree but a few examples (like turbChannel) should demonstrate how to use CHAR.

…

-----Original message-----

From:fischer1 ***@***.***> Sent: Saturday 27th January 2018 5:31 To: Nek5000/NekExamples ***@***.***> Cc: Subscribed ***@***.***> Subject: [Nek5000/NekExamples] IFCHAR = T ?? (#100) I notice that several examples have ifchar=T. Some don't even use a dt big enough to warrant such usage (e.g., cyl_restart case). I think all examples (except for short tests designed to test Characteristics) should have IFCHAR F unless we really want to show off CFL >> 1. Otherwise, jobs will run twice as slow. People often start with one of the examples and modify it to suit their needs without realizing that IFCHAR=T. (This happened in one of the large KTH runs that George did for pipe flow. He was running with CFL=0.5 and IFCHAR T. Turning that to F sped the code up by 2X and would have saved a million core hours---it was my fault for not paying attention earlier that time.) Can we / should we switch all the examples to have default IFCHAR F (since the decision to use Characteristics is typically a more advanced-user decision) ? � You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#100>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ARumf57D91XFN4Ebezy5Cso9QMWYt6Mhks5tOqaHgaJpZM4RvJIl>.

[fischer1]

Yes - we definitely want examples that demo ifchar.

I was just surprised (and I'm sure it's my fault) that ext_cyl had IFCHAR T yet the CFL was 0.5

So, I grepped "IFCHAR" in all the /.rea files and saw that there were other places
where it was true. Given that the overhead his potentially expensive, we probably
want to notify users which cases have IFCHAR T --- turbchannel is a good one.

[adampep]

Right now there are 5 examples using characteristics on purpose: Pipe_Stenosis, TurbJet, TurbChannel, TurbPipe and Vortex. I removed the rest of the flags except Os7000, as in this case delta in the test is so small, that the test crushes even though cfl=0.475. What was the source of the test value in this case?