SNESComputeJacobianDefaultColor#

Computes the Jacobian using finite differences and coloring to exploit matrix sparsity.

Synopsis#

#include "petscsnes.h"  
#include "petscdm.h"    
PetscErrorCode SNESComputeJacobianDefaultColor(SNES snes, Vec x1, Mat J, Mat B, void *ctx)

Collective

Input Parameters#

snes - nonlinear solver object
x1 - location at which to evaluate Jacobian
ctx - MatFDColoring context or NULL

Output Parameters#

J - Jacobian matrix (not altered in this routine)
B - newly computed Jacobian matrix to use with preconditioner (generally the same as J)

Options Database Keys#

-snes_fd_color_use_mat - use a matrix coloring from the explicit matrix nonzero pattern instead of from the DM providing the matrix
-snes_fd_color - Activates SNESComputeJacobianDefaultColor() in SNESSetFromOptions()
-mat_fd_coloring_err - Sets (square root of relative error in the function)
-mat_fd_coloring_umin - Sets umin, the minimum allowable u-value magnitude
-mat_fd_type - Either wp or ds (see MATMFFD_WP or MATMFFD_DS)
-snes_mf_operator - Use matrix free application of Jacobian
-snes_mf - Use matrix free Jacobian with no explicit Jacobian representation

Notes#

If the coloring is not provided through the context, this will first try to get the coloring from the DM. If the DM has no coloring routine, then it will try to get the coloring from the matrix. This requires that the matrix have its nonzero locations already provided.

SNES supports three approaches for computing (approximate) Jacobians: user provided via SNESSetJacobian(), matrix-free via SNESSetUseMatrixFree(), and computing explicitly with finite differences and coloring using MatFDColoring. It is also possible to use automatic differentiation and the MatFDColoring object, see src/ts/tutorials/autodiff/ex16adj_tl.cxx

This function can be provided to SNESSetJacobian() along with an appropriate sparse matrix to hold the Jacobian