On 11/29/2017 09:39 PM, Jie Cheng wrote:
Here is what I suspect: Method 1 uses the stiffness_matrix that has been
modified during the assembly, while method 2 is using the original
stiffness. Although method 2 will eventually distribute the rhs vector
as well as the matrix, it is distributed along with system_matrix, not
stiffness_matrix. In the time-dependent simulation, those two are
different. I don't know if the modifications to the rhs vector depends
on the matrix or not.
For hanging nodes they do. For non-zero boundary values the same applies
(see video lectures 21.6 and 21.65 to understand why).
I would have to think for a while to figure out what exactly is going on
in your case, and how to make sure you get the same results, but don't
have the necessary time for this. I think that if you look through the
video lectures references above, you'll see what one of the two methods
you use is doing, and that may help you understand what you need to do
to get things right.
Best
W.
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Wolfgang Bangerth email: bange...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/
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