[evgenii]

Hi, everyone!

I have a question about syntax. In anlitycalCylinder (from tutorials) I came across next code

U.boundaryField()[3][0].x()
U.mesh().boundary()[4].Cf()[0]

What do [3][0] in the first case and [4]...[0] in the second case mean? Is it a some kind of element indexing? I've read Guides very attentively, but unfortunately there is no information at all.

Hope to get some help.

[eugene]

It is indeed indexing.

U.boundaryField()[3][0].x()
This is the x component of velocity for face number 0 from boundary region number 3. I.e. the first index accesses a specific boundary region of the U field, while the second addresses the face within that region.

U.mesh().boundary()[4].Cf()[0]
This is the face centre vector for face number 0 from boundary region number 4.

[evgenii]

I was thinking something like that, but I wanted to be sure

Thank you for reply