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<div id="version" align=right><b>petsc-3.14.5 2021-03-03</b></div>
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<A NAME="SNESComputeJacobianDefault"><H1>SNESComputeJacobianDefault</H1></A>
Computes the Jacobian using finite differences.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscsnes.h"
<A HREF="../Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> <A HREF="../SNES/SNESComputeJacobianDefault.html#SNESComputeJacobianDefault">SNESComputeJacobianDefault</A>(<A HREF="../SNES/SNES.html#SNES">SNES</A> snes,<A HREF="../Vec/Vec.html#Vec">Vec</A> x1,<A HREF="../Mat/Mat.html#Mat">Mat</A> J,<A HREF="../Mat/Mat.html#Mat">Mat</A> B,void *ctx)
</PRE>
Collective on <A HREF="../SNES/SNES.html#SNES">SNES</A>
<P>
<H3><FONT COLOR="#CC3333">Input Parameters</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>x1 </B></TD><TD>- compute Jacobian at this point
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>ctx </B></TD><TD>- application's function context, as set with <A HREF="../SNES/SNESSetFunction.html#SNESSetFunction">SNESSetFunction</A>()
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Output Parameters</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>J </B></TD><TD>- Jacobian matrix (not altered in this routine)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>B </B></TD><TD>- newly computed Jacobian matrix to use with preconditioner (generally the same as J)
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Options Database Key</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-snes_fd </B></TD><TD>- Activates <A HREF="../SNES/SNESComputeJacobianDefault.html#SNESComputeJacobianDefault">SNESComputeJacobianDefault</A>()
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-snes_test_err </B></TD><TD>- Square root of function error tolerance, default square root of machine
epsilon (1.e-8 in double, 3.e-4 in single)
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-mat_fd_type </B></TD><TD>- Either wp or ds (see <A HREF="../Mat/MATMFFD_WP.html#MATMFFD_WP">MATMFFD_WP</A> or <A HREF="../Mat/MATMFFD_DS.html#MATMFFD_DS">MATMFFD_DS</A>)
</TD></TR></TABLE>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
This routine is slow and expensive, and is not currently optimized
to take advantage of sparsity in the problem. Although
<A HREF="../SNES/SNESComputeJacobianDefault.html#SNESComputeJacobianDefault">SNESComputeJacobianDefault</A>() is not recommended for general use
in large-scale applications, It can be useful in checking the
correctness of a user-provided Jacobian.
<P>
An alternative routine that uses coloring to exploit matrix sparsity is
<A HREF="../SNES/SNESComputeJacobianDefaultColor.html#SNESComputeJacobianDefaultColor">SNESComputeJacobianDefaultColor</A>().
<P>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../SNES/SNESSetJacobian.html#SNESSetJacobian">SNESSetJacobian</A>(), <A HREF="../SNES/SNESComputeJacobianDefaultColor.html#SNESComputeJacobianDefaultColor">SNESComputeJacobianDefaultColor</A>(), <A HREF="../SNES/MatCreateSNESMF.html#MatCreateSNESMF">MatCreateSNESMF</A>()
<BR><P><B></B><H3><FONT COLOR="#CC3333">Level</FONT></H3>intermediate<BR>
<H3><FONT COLOR="#CC3333">Location</FONT></H3>
</B><A HREF="../../../src/snes/interface/snesj.c.html#SNESComputeJacobianDefault">src/snes/interface/snesj.c</A>
<P><H3><FONT COLOR="#CC3333">Examples</FONT></H3>
<A HREF="../../../src/ts/tutorials/ex4.c.html">src/ts/tutorials/ex4.c.html</A><BR>
<A HREF="../../../src/ts/tutorials/ex10.c.html">src/ts/tutorials/ex10.c.html</A><BR>
<A HREF="../../../src/ts/tutorials/ex15.c.html">src/ts/tutorials/ex15.c.html</A><BR>
<A HREF="../../../src/ts/tutorials/ex17.c.html">src/ts/tutorials/ex17.c.html</A><BR>
<BR><A HREF="./index.html">Index of all SNES routines</A>
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