about MatMult()

[Yujie]

the following is about MatMult() in manual.
"
The parallel matrix can multiply a vector with n local entries, returning a
vector with m local entries.
That is, to form the product
MatMult(Mat A,Vec x,Vec y);
the vectors x and y should be generated with
VecCreateMPI(MPI Comm comm,n,N,&x);
VecCreateMPI(MPI Comm comm,m,M,&y);
"
I am wondering whether I must create Vector "y" before I call MatMult()
regardless of parrellel and sequentail modes?
thanks a lot.

Regards,
Yujie
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