Nek5000
IFCHAR = T ??
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) ?
I agree but a few examples (like turbChannel) should demonstrate how to use CHAR.
-----Original message-----
From:fischer1 [email protected] Sent: Saturday 27th January 2018 5:31 To: Nek5000/NekExamples [email protected] Cc: Subscribed [email protected] 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 https://github.com/Nek5000/NekExamples/issues/100, or mute the thread https://github.com/notifications/unsubscribe-auth/ARumf57D91XFN4Ebezy5Cso9QMWYt6Mhks5tOqaHgaJpZM4RvJIl.
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.
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?
