Junchao, If you need to access off-process values and put them into a new vector, you should use VecScatter.
"Smith, Barry F." <[email protected]> writes: > Setting large contiguous blocks of values is not a common use case. In > finite elements the values are not contiguous. > >> On Apr 20, 2018, at 3:45 PM, Zhang, Junchao <[email protected]> wrote: >> >> I agree the extra overhead can be small, but users are forced to write a >> loop where one single line gives the best. >> >> --Junchao Zhang >> >> On Fri, Apr 20, 2018 at 3:36 PM, Smith, Barry F. <[email protected]> wrote: >> >> When setting values into matrices and vectors we consider the "extra" >> overhead of needing to pass in the indices for all the values (instead of >> being able to set an arbitrary block of values without using indices for >> each one) to be a minimal overhead that we can live with. >> >> Barry >> >> >> > On Apr 20, 2018, at 3:33 PM, Junchao Zhang <[email protected]> wrote: >> > >> > >> > On Fri, Apr 20, 2018 at 3:18 PM, Matthew Knepley <[email protected]> wrote: >> > On Fri, Apr 20, 2018 at 4:10 PM, Junchao Zhang <[email protected]> wrote: >> > To pad a vector, i.e., copy a vector to a new one, I have to call >> > VecSetValue(newb,1,&idx,...) for each element. But to be efficient, what I >> > really needs is to set a block of values in one call. It looks PETSc does >> > not have a routine for that(?). I looked at VecSetValuesBlocked, but it >> > looks it is not for that purpose. >> > Should we have something like VecSetValuesBlock(Vec v,PetscInt i,PetscInt >> > cnt,PetscScalar *value, InsertMode mode) to set cnt values starting at >> > index i? >> > >> > Use VecGetArray(). >> > Did you mean VecGetArray b and newb, do a memcpy from b to new and then >> > restore them? If yes, it does not work since some of the values I want to >> > set might be remote. >> > E.g, I have 4 processors. b's size is 181 and is distributed as 46, >> > 45,45,45, newb is distributed as 48,45,45,45 to match a matrix of block >> > size 3. >> > >> > >> > Matt >> > >> > --Junchao Zhang >> > >> > >> > >> > -- >> > What most experimenters take for granted before they begin their >> > experiments is infinitely more interesting than any results to which their >> > experiments lead. >> > -- Norbert Wiener >> > >> > https://www.cse.buffalo.edu/~knepley/ >> > >> >>
