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<A NAME="MATSNESMF_WP"><H1>MATSNESMF_WP</H1></A>
Implements an alternative approach for computing the differencing parameter h used with the finite difference based matrix-free Jacobian. This code implements the strategy of M. Pernice and H. Walker: h = error_rel * sqrt(1 + ||U||) / ||a||
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<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
1) || U || does not change between linear iterations so is reused
2) In GMRES || a || == 1 and so does not need to ever be computed except at restart
when it is recomputed.
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Reference: M. Pernice and H. F. Walker, "NITSOL: A Newton Iterative
Solver for Nonlinear Systems", SIAM J. Sci. Stat. Comput.", 1998,
vol 19, pp. 302--318.
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<H3><FONT COLOR="#CC3333">Options Database Keys</FONT></H3>
<DT><B>-snes_mf_compute_normu </B> -Compute the norm of u everytime see <A HREF="../SNESMF/MatSNESMFWPSetComputeNormU.html#MatSNESMFWPSetComputeNormU">MatSNESMFWPSetComputeNormU</A>()
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Notes: Requires no global collectives when used with GMRES
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<H3><FONT COLOR="#CC3333">Formula used</FONT></H3>
F'(u)*a = [F(u+h*a) - F(u)]/h where
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<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../SNESMF/MATMFFD.html#MATMFFD">MATMFFD</A>, <A HREF="../SNESMF/MatCreateMF.html#MatCreateMF">MatCreateMF</A>(), <A HREF="../SNESMF/MatCreateSNESMF.html#MatCreateSNESMF">MatCreateSNESMF</A>(), <A HREF="../SNESMF/MATSNESMF_DS.html#MATSNESMF_DS">MATSNESMF_DS</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/snes/mf/wp.c.html#MATSNESMF_WP">src/snes/mf/wp.c</A>
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