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<A NAME="MATMFFD_DS"><H1>MATMFFD_DS</H1></A>
the code for compute the "h" used in the finite difference matrix-free matrix vector product. This code implements the strategy in Dennis and Schnabel, "Numerical Methods for Unconstrained Optimization and Nonlinear Equations".
<H3><FONT COLOR="#CC3333">Options Database Keys</FONT></H3>
<DT><B>-mat_mffd_umin <umin> see <A HREF="../Mat/MatMFFDDSSetUmin.html#MatMFFDDSSetUmin">MatMFFDDSSetUmin</A>()</B> -
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<P>
Notes: Requires 2 norms and 1 inner product, but they are computed together
so only one parallel collective operation is needed. See <A HREF="../Mat/MATMFFD_WP.html#MATMFFD_WP">MATMFFD_WP</A> for a method
(with GMRES) that requires NO collective operations.
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<H3><FONT COLOR="#CC3333">Formula used</FONT></H3>
F'(u)*a = [F(u+h*a) - F(u)]/h where
h = error_rel*u'a/||a||^2 if |u'a| > umin*||a||_{1}
= error_rel*umin*sign(u'a)*||a||_{1}/||a||^2 otherwise
where
error_rel = square root of relative error in function evaluation
umin = minimum iterate parameter
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<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../Mat/MATMFFD.html#MATMFFD">MATMFFD</A>, <A HREF="../Mat/MatCreateMFFD.html#MatCreateMFFD">MatCreateMFFD</A>(), <A HREF="../SNES/MatCreateSNESMF.html#MatCreateSNESMF">MatCreateSNESMF</A>(), <A HREF="../Mat/MATMFFD_WP.html#MATMFFD_WP">MATMFFD_WP</A>, <A HREF="../Mat/MatMFFDDSSetUmin.html#MatMFFDDSSetUmin">MatMFFDDSSetUmin</A>()
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<P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>intermediate
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/mat/impls/mffd/mffddef.c.html#MATMFFD_DS">src/mat/impls/mffd/mffddef.c</A>
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