[petsc-users] coordinate point location in mesh

[Matthew Knepley]

On Fri, Apr 5, 2013 at 2:33 PM, Dharmendar Reddy <dharmareddy84 at gmail.com>wrote:

> Hello
>         Do i am currently cloned petsc using git. Looks like the function
> you mentioned is in knepley/pylith. How do i switch to that branch ?
> I guess i need to pull the branch before switching ?
> git branch knepley/pylith
> and
> reconfigure ?
>
> May not be of (immediate) concern but an observation about the
> LocatePoint_<Simplex> codes.
>
> I see that test is done for every cell by calculating the ref cell mapped
> coordinates for a given point. It might help speed up things if there is a
> test to first check if the given point is with in the square/cube
> containing the simplex.
>

That does not change the order of the method. So far, this had not been
worth optimizing, since its a very small fraction of time (< 1%).
When it gets optimized, we will use a hierarchical division like a kd-tree.

  Thanks,

     Matt


> The above test will make sure that the point is inside the cell or with in
> one of the adjoining cells.
>
> I am assuming the DMPlex object has information about cells adjoining a
> given cell. Since the LocatePoint_<Simplex> calculates the ref cell mapped
> coordinates, I may be wrong here but i am thinking we can use that
> information to check outside which facet of the refcell the given point is
> and then try to locate the point in the cell sharing that facet.
>
> Thanks
> Reddy
>
> On Thu, Apr 4, 2013 at 3:37 PM, Matthew Knepley <knepley at gmail.com> wrote:
>
>> On Fri, Apr 5, 2013 at 6:29 AM, Dharmendar Reddy <dharmareddy84 at gmail.com
>> > wrote:
>>
>>> Hello,
>>>          Is there any DMPlex function which will tell me to which DMPlex
>>> point a given coordinate point  belongs to ?
>>> I am looking for cell id given a coordinates of a point.
>>>
>>
>> I have experimental code to do this, DMPlexLocatePoint(). There are
>> tests, but they are not that stringent for
>> hexes. Let me know if this works for you.
>>
>>    Matt
>>
>>
>>> If not,  I can think of writing of a test for point in cell
>>> and loop over cells to find the cell id. Any suggestions for doing this
>>> ?
>>>
>>>
>>> The physical problem i am looking at is a Poisson equation in a given
>>> domain.
>>>
>>> - \Delta u(x) = rho(x)  where rho is a sum of delta functions randomly
>>> located in the domain.
>>> --
>>> -----------------------------------------------------
>>> Dharmendar Reddy Palle
>>> Graduate Student
>>> Microelectronics Research center,
>>> University of Texas at Austin,
>>> 10100 Burnet Road, Bldg. 160
>>> MER 2.608F, TX 78758-4445
>>> e-mail: dharmareddy84 at gmail.com
>>> Phone: +1-512-350-9082
>>> United States of America.
>>> Homepage: https://webspace.utexas.edu/~dpr342
>>>
>>
>>
>>
>> --
>> What most experimenters take for granted before they begin their
>> experiments is infinitely more interesting than any results to which their
>> experiments lead.
>> -- Norbert Wiener
>>
>
>
>
> --
> -----------------------------------------------------
> Dharmendar Reddy Palle
> Graduate Student
> Microelectronics Research center,
> University of Texas at Austin,
> 10100 Burnet Road, Bldg. 160
> MER 2.608F, TX 78758-4445
> e-mail: dharmareddy84 at gmail.com
> Phone: +1-512-350-9082
> United States of America.
> Homepage: https://webspace.utexas.edu/~dpr342
>



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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