[petsc-users] A Question about Vec

[Ryan Yan]

Hi Satish,
Thank you very much for the crystal clear explanation.

Yan


On Thu, Feb 4, 2010 at 12:24 AM, Satish Balay <balay at mcs.anl.gov> wrote:

> On Wed, 3 Feb 2010, Ryan Yan wrote:
>
> > Hi all,
> > Can someone help me to understand the "Vec"?
> >
> > My question is: in the following piece of code, will "a" be changed, if
> "b"
> > is changed by the subroutine "SNESComputeFunction"? I did see that both a
> > and b are both pointers to an object.
>
> Yes - all petsc datatypes [Vec,Mat etc..] are pointers to [opaque] objects.
>
> >
> > Vec a = b;
>
> So you can make copy of this pointer - and use it aswell.
>
> > Vec c;
> >
> > initalize c;
> > SNESComputeFunction(snes, c, b);
> >
> > If the answer is yes, then I guess what is modified is actually "*b" in
> the
> > above code, is that right?
>
> yes - the object [refered by this pointer] is modified.
>
> > BTW, I am wondering is there any explicit way that one can compare two
> > variables in the instance above in PETSc , especially when the content of
> > the object is rich.
>
> In the above case - if you are carrying multiple copies of pointers
> arround - you just check the pointers. [ a == b]
>
> The alternative is having multiple objects.
>
> Vec a, b
>
> <create a>
> <set values in a>
>
> VecDuplicate(a,&b)
> VecCopy(a,b)
> VecEqual(a,b,flag)
>
> Here 'a','b' are different vecs - so if a is modified - it has no relation
> to values of 'b'
>
> Satish
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20100204/bf07236c/attachment.htm>