DOLFIN

misleading Cell::diameter()

Bug #1132490 reported by Jan Blechta
10
This bug affects 2 people
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DOLFIN
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Bug Description

Cell::diameter() returns two times circumradius. I think correct way would be to return length of a longest edge (for simplices) as it is consistent with a normal use of term "diameter" in mathematics, see http://mathworld.wolfram.com/GeneralizedDiameter.html. Presently implemented diameter can return arbitrarily large values as cells' true diameter remains bounded.

This issue is related to bug 1082157 and bug 948379.

I think changing Cell::diameter() to the length of a longest edge (and moving the existing computation to Cell::circumradius()) would solve all isssues of this kind and prevent some confussion in a future. I would take care of this in case of agreement.

EDIT: Warning: as this kind of change or similiar is done CellType::radius_ratio() implementtation needs updating as it assumes that diameter() returns 2.*circumradius!

See original description
Jan Blechta (blechta)
description: updated
Revision history for this message
Nico Schlömer (nschloe) wrote :

If it's confusing, the function name 'diameter' should probably be banned entirely, and replaced by "circumradius()" and "max_edge()" or similar.

Revision history for this message
Jan Blechta (blechta) wrote : Re: [Bug 1132490] Re: misleading Cell::diameter()

On Tue, 19 Mar 2013 18:17:05 -0000
Nico Schlömer <email address hidden> wrote:
> If it's confusing, the function name 'diameter' should probably be
> banned entirely, and replaced by "circumradius()" and "max_edge()" or
> similar.
>

That's probably not good idea as function diameter() is used in working
DG codes.

For clarification I suggest that diameter() would calculate a quantity
which we call diameter in mathematics (that would be max edge length
for simplices). Existing calculation of diameter of a circumscribed
sphere would be moved to new function called circumradius().

What I consider confusing is that diameter() calculates a quantity
which can be arbitrarily larger than diameter!

Still, I'm waiting for some response to start a work.

Jan

description: updated
Jan Blechta (blechta)
description: updated
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