Hello,

My run function is calling the assemble_system_matrix. 

I have implemented a new method that is supposedly allow us to assemble the 
system matrix only once at the beginning saving comp time. Our variables 
are solved sequentially and implicitly and I have a boolean that indicates 
whether we use this new method or not. in one of the variables, I have 
added stability term that, mathematically speaking, should make our method 
for solving one of the variables explicit rather than implicit. From what I 
know currently, dealii is assembling the matrix at every time step 
regardless if I say I am using the new method or not. Should I have to 
modifiy how the assemble_system_matrix function is called in the run 
function or should I modify the header file that actually computes the 
assembly of the matrix? Not sure on how to proceed.

Thanks,
Mark
On Thursday, August 22, 2024 at 4:55:38 PM UTC-5 Wolfgang Bangerth wrote:

>
> On 8/22/24 15:42, Mark Simmons wrote:
> > 
> > 1.) can I check to see if deal.ii is actually reassembling my matrix at 
> > every time step?
> > 2.) how can I make sure that my matrix is only assembled once at the 
> > beginning?
>
> deal.II is not calling functions behind your back. If your run() 
> function is not calling assemble_system(), then assemble_system() is not 
> called.
>
> But if you want to make sure, why don't you just put something like
> std::cout << "********* ASSEMBLING MATRIX ***********" << std::endl;
> at the top of the function that assembles the matrix? Then you just have 
> to read through your program's output to see where that function is 
> apparently executed.
>
> Best
> W.
>

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