[Nek5000-users] explstrs routine

[nek5000-users at lists.mcs.anl.gov]

On Fri, 29 Jul 2011, nek5000-users at lists.mcs.anl.gov wrote:

> Paul,
>
> Ah, yes, I see it now.  Basically, you WOULD need two 1/J 's in the
> computation, but yes, I was forgetting that w3m1 is just the weights
> without the Jacobian added in.  So J will cancel out one of the 1/J's.
>
> Thanks!
>
> On Fri, Jul 29, 2011 at 10:32 PM,  <nek5000-users at lists.mcs.anl.gov> wrote:
>>
>> Hi Josh,
>>
>> You need the jacobian at least once, since normally:
>>
>>   B = w3m1*Jac
>>
>> Does this make sense?
>>
>> Paul
>>
>>
>> On Fri, 29 Jul 2011, nek5000-users at lists.mcs.anl.gov wrote:
>>
>>> Hello Neks
>>>
>>> I came across the routine explstrs (and its subroutines) while
>>> exploring the code (and with the recommendation from Paul).  I
>>> understand that it is essentially performing something like
>>>
>>>  D^T * B * D * [u]
>>>
>>> I had a question about the use of the Jacobian in the routine
>>> expl_strs_e_3d (or _2d).  Following the routine, I can see where it
>>>
>>> 1) Computes the gradients w.r.t. r, s, t   (gradl_rst)
>>>
>>> 2) Multiplies these gradients by appropriate coordinate derivatives
>>> (rxm1, tzm1, etc)
>>>
>>> 3) Multiplies these results by the quadrature weights. (from w3m1)
>>>
>>> 4) Multiplies these results again by the coordinate transformations,
>>> and then apply the transpose operation (gradl_rst_t)
>>>
>>> When I look in coef.f, I see that when dr/dx, ds/dx, etc. are computed
>>> from dx/dr, dy/ds, etc., the inverse of the Jacobian is not applied
>>> yet.  So, I can see why jacmi is multiplied along with w3m1 when
>>> multiplying by the quadrature weights.
>>>
>>> My question is, would we not need to multiply again by jacmi when the
>>> transpose derivative operator is applied (because of the use of rxm1,
>>> sxm1, etc)?  Is this something that is applied later on, or am I
>>> missing something and it isn't necessary to apply it again?
>>>
>>> Thank you,
>>>
>>> Josh
>>>
>>> --
>>> Josh Camp
>>>
>>> "All that is necessary for the triumph of evil is that good men do
>>> nothing" -- Edmund Burke
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>
>
>
> -- 
> Josh Camp
>
> "All that is necessary for the triumph of evil is that good men do
> nothing" -- Edmund Burke
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