[petsc-users] Problems about fd_coloring

[Yingjie Wu]

Dear PETSc developers:
Hi,
I want to try some of the operations of matrix coloring. I have written a
model of a system of non-linear equations and solved it using - snes_fd, so
there is no Compute_Jacobian routine. Previous developers suggested that I
use:
 -snes_fd_color -snes_fd_color_use_mat -mat_coloring_type greendy
to improve computational efficiency. I know little about coloring. It seems
to be a way to store the matrix structure, so that when the finite
difference routine is used, the difference can be calculated only at the
position of non-zero elements of Jacobian matrix, avoiding the difference
calculation of "0" elements. I don't know if I understand this correctly.


My program is a two-dimensional problem, but it does not use the DM object
to allocate the solution vector X. Is there any problem with fd_coloring?


For users like me who don't know coloring, how should I get some usage
methods? It seems that the instructions on manual are somewhat brief.

In addition, because Matrix Free needs an efficient Preconditioner and
because some complex parameter variables make it impossible for me to
analytically construct Jacobian matrices, the finite difference
approximation of Jacobian matrices may be the most appropriate method at
present.The reason I want to know about fd_coloring is to improve
computational efficiency.

I hope to get your advice.

Thanks,
Yingjie
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