[petsc-users] customized MatMult

[Marco Cisternino]

Good morning, 
I'm writing my MatMult function, but I don't know how to treat the ghost elements of the result vec. Let's say myMatMult(A,x,y). 

First question is: if I use my MatMult in a KSP to solve a linear system, do I have to update ghost elements in the result vec of MatMult?? Consider that any time the code enters myMatMult the vec x is copied in my container and the ghost of my container are updated. I made computation for matrix-vector and I copied the results in vec y, without considering ghost elements of y. 

Second question: if I have to, how? 
Let's say I state: 
ierr = myMatMult(A,x,y) ; 
and x has been built out of myMatMult with VecGhostCreate. 
How do I update ghost elements of y in myMatMult? VecGhostUpdateBegin/VecGhostUpdateEnd in myMatMult? 

Any hints would be appreciated. 
Thanks for you advices in advance. 

Bests, 

Marco 
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