About `dolfinx.fem.petsc.assemble_matrix` API

[lyunfei1211]

There are two APIs aboutthe matrix assembling operation in dolfinx 0.9.0.

The above one has no parameter A: Mat, and the bellow has it. What is the difference between them? And again the intruction for Parameters has no A: Mat. When I use the following sentences

the code editor prompts Unexpected argument .
So how can I use the function with parameter A: Mat?

[dokken]

The one with A as input expects a PETS Matrix that you will add the contributions of the form a to. This is useful if you need too assemble the matrix multiple times, is it avoids reallocation of memory.

See for instance

python/test/unit/fem/test_bcs.py

Test problem 2: Flow past a cylinder (DFG 2D-3 benchmark) — FEniCSx tutorial (Step 1 in temporal loop)
The standard way of compiling code with DOLFINx — FEniCS Workshop

[lyunfei1211]

Thanks for your comments, Mr. dokken.
By the way, when using the function

@dokken

assemble_matrix(A, a, bcs=bcs)

is it required to call A.assemble() after the sentence to get the matrix assembled?

[dokken]

That is required for both APIs. It takes care of the parallel communication/accumulation of data.