You are correct, I was wrong. It returns the 2 norm (not the square of the 2 norm).
Barry > On Aug 1, 2016, at 2:59 PM, Xiangdong <[email protected]> wrote: > > > > On Fri, Jul 29, 2016 at 10:41 AM, Barry Smith <[email protected]> wrote: > > > On Jul 27, 2016, at 4:42 PM, Xiangdong <[email protected]> wrote: > > > > Hello everyone, > > > > I have a global dmda vector vg. On each processor, if I want to know the > > norm of local portion of vg, which function should I call? > > > > So far I am thinking of using DMDAVecGetArray and then write a loop to > > compute the norm of this local array. > > > > Is there a simple function available to call? like > > *vg->ops->norm_local(vg,NORM_2, &normlocal)? > > There isn't a public interface to this call because it really isn't a > mathematically well defined object; the subdomains in the decomposition of > the array are arbitrary based on the number of processes used. > > Anyways if you want it and it is the NON-overlapping portion then yes, you > can write a little routine (basically just cut and paste VecNorm()) call it > say VecNormLocal() and have it call the function pointer you indicated above. > Note for the 2 norm the norm_local() returns the square of the norm so you > need to take the square root. > > I am interested in this non-overlapping case. I found that this norm_local() > function returns the correct l2 norm, not the square of norm. I am using old > version 3.5. Are there changes in recent version such that norm_local() > returns the square of the norm? > > Xiangdong > > > If you want the overlapping portion of the vector then you should just do > the DMDAVecGetArray() as you already do. > > Barry > > > > > > > Thanks. > > > > Best, > > Xiangdong > >
