<p>To keep the stencil small for matrix preallocation, you can create two DMDAs.</p>
<div class="gmail_quote">On Jan 6, 2012 9:07 PM, "Barry Smith" <<a href="mailto:bsmith@mcs.anl.gov">bsmith@mcs.anl.gov</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
On Jan 6, 2012, at 4:43 PM, Xuefeng Li wrote:<br>
<br>
> On Fri, 6 Jan 2012, Matthew Knepley wrote:<br>
><br>
>> On Fri, Jan 6, 2012 at 4:32 PM, Xuefeng Li <<a href="mailto:li@loyno.edu">li@loyno.edu</a>> wrote:<br>
>><br>
>>> However, is there a way to change/adjust the stencil width<br>
>>> AFTER the DA has been created and set up to a DMMG? Or,<br>
>>> in general, can we attach different DA objects to a DMMG<br>
>>> at different times?<br>
>>><br>
>><br>
>> 1) You cannot change this after setting up the DA. Just make another DA,<br>
>> since<br>
>> they are very lightweight.<br>
>><br>
>> 2) I think structuring new code around DMMG is wrong. It has been removed in<br>
>> petsc-dev and is deprecated in 3.2. What are you trying to do?<br>
>><br>
> I am just trying to use the ghost points to share<br>
> data among neighboring processes at one step<br>
> during the whole iteration. At that particular<br>
> step, the stencil width needs to be bigger.<br>
><br>
> One can always set the stencil width to be big<br>
> enough so that one does not need to adjust it.<br>
> But this is just not as efficient as it can be.<br>
<br>
Just create a bigger-stencil DMDA that you use during those "special" steps.<br>
<br>
Barry<br>
<br>
><br>
> Thanks again.<br>
><br>
> Regards,<br>
><br>
> --Xuefeng Li, <a href="tel:%28504%29865-3340" value="+15048653340">(504)865-3340</a>(phone)<br>
> Like floating clouds, the heart rests easy<br>
> Like flowing water, the spirit stays free<br>
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><br>
<br>
</blockquote></div>