petsc-3.4.5 2014-06-29

SNESComputeJacobianDefault

Computes the Jacobian using finite differences.

Synopsis

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

Collective on SNES

Input Parameters

	x1	- compute Jacobian at this point
	ctx	- application's function context, as set with SNESSetFunction()

Output Parameters

	J	- Jacobian matrix (not altered in this routine)
	B	- newly computed Jacobian matrix to use with preconditioner (generally the same as J)
	flag	- flag indicating whether the matrix sparsity structure has changed

Options Database Key

	-snes_fd	- Activates SNESComputeJacobianDefault()
	-snes_test_err	- Square root of function error tolerance, default square root of machine epsilon (1.e-8 in double, 3.e-4 in single)
	-mat_fd_type	- Either wp or ds (see MATMFFD_WP or MATMFFD_DS)

Notes

This routine is slow and expensive, and is not currently optimized to take advantage of sparsity in the problem. Although SNESComputeJacobianDefault() is not recommended for general use in large-scale applications, It can be useful in checking the correctness of a user-provided Jacobian.

An alternative routine that uses coloring to exploit matrix sparsity is SNESComputeJacobianDefaultColor().

Keywords

SNES, finite differences, Jacobian

Examples

src/ts/examples/tutorials/ex4.c.html
src/ts/examples/tutorials/ex10.c.html
src/ts/examples/tutorials/ex15.c.html
src/ts/examples/tutorials/ex17.c.html