Re: [Libmesh-users] question on Trapezoidal integration rule

[Michael P. <mpo...@pu...>]

On 11/07/2018 04:02 PM, Stogner, Roy H wrote:
> On Wed, 7 Nov 2018, Michael Povolotskyi wrote:
>
>> On 11/07/2018 02:59 PM, Stogner, Roy H wrote:
>>>   On Wed, 7 Nov 2018, Michael Povolotskyi wrote:
>>>
>>>>   if I use the trapezoidal rule:
>>>>
>>>>   QTrap qrule(dim)
>>>>
>>>>   Can I assume the quadrature points are ordered in the same way at the
>>>>   element
>>>>   nodes?
>>>   Doesn't look that way, in general, at first glance.  We build the quad
>>>   and hex QTrap rules via tensor products, but that's not how we order
>>>   nodes.
>>>   ---
>>>   Roy
>> Thank you,
>> then how to solve the following problem.
>>
>> I have an element that has n_nodes;
>> It has the same number of quadrature points that are at the nodal positions
>> (trapezoidal rule is assumed).
>> How to find the node number that corresponds to a quadrature point?
>> Should I compare coordinates?
> If you do that at runtime then it will throw a ton of unnecessary
> calculation into an inner loop.  You could just hardcode the
> permutation vectors; looking over quadrature_trap*.C it looks like
> (mapping from quadrature point numbers to node numbers, and don't
> trust me on this without verifying it):
>
> QUAD4: {0, 1, 3, 2}
> HEX8:  {0, 1, 3, 2, 4, 5, 7, 6}
>
> And then edge/triangle/prism elements are all the identity
> permutation... and we don't support QTrap on pyramids apparently?
> ---
> Roy
Thank you,
I'll code a permutation vector inside my application.
Michael.