[petsc-users] How to do the preallocation and set zeros to rows and columns?

[Dongyu Liu - CITG via petsc-users]

Hi,


I am using PETSc to run FEM on domain decomposition. When I assemble the 
matrix, I need to pre-allocate first to get better performance, can you 
recommend how to preallocate in this case?


Right now we set big values for the number of nonzeros to preallocate memory, 
but when we do so, the program stuck at setZeroRowColumns. The error message is 
like:

Matrix is missing diagonal entry in row 2.


Do you have any idea why this happens?

Note: In the domain decomposition we used, processors share some nodes.


Best,

Dongyu