[petsc-users] VecNorm() of VECNEST returns 0 while sub-vectors have nonzero norms

[Pierre Jolivet]

Could you please share a runnable piece of code?
I’ve tried to generate an example myself, and I don’t get 0 for the norm of G.

Thanks,
Pierre

> On 6 Jan 2026, at 11:12 AM, Michael Wick <michael.wick.1980 at gmail.com> wrote:
> 
> Hello PETSc users,
> 
> I have a VECNEST norm issue and would appreciate help.
> 
> I create a nest vector:
> VecCreateNest(PETSC_COMM_WORLD, 2, NULL, subG, &G);
> 
> But:
> VecNorm(G, NORM_2, &nG) returns 0
> 
> While the sub-vectors are clearly nonzero:
> VecNestGetSubVec(G,0,&v0); VecNorm(v0,NORM_2,&n0); // n0 > 0
> VecNestGetSubVec(G,1,&v1); VecNorm(v1,NORM_2,&n1); // n1 > 0
> 
> Can someone give a hint on what might go wrong?
> 
> Thanks,
> 
> M
> 

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