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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="SNESLINESEARCHBT"><H1>SNESLINESEARCHBT</H1></A>
Backtracking line search. This line search finds the minimum of a polynomial fitting of the L2 norm of the
function or the objective function if it is provided with <A HREF="../SNES/SNESSetObjective.html#SNESSetObjective">SNESSetObjective</A>(). If this fit does not satisfy the conditions for progress, the interval shrinks
and the fit is reattempted at most max_it times or until lambda is below minlambda.
<P>
<H3><FONT COLOR="#CC3333">Options Database Keys</FONT></H3>
<TABLE border="0" cellpadding="0" cellspacing="0">
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-snes_linesearch_alpha <1e-4> </B></TD><TD>- slope descent parameter
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-snes_linesearch_damping <1.0> </B></TD><TD>- initial step length
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-snes_linesearch_maxstep <length> </B></TD><TD>- if the length the initial step is larger than this then the
step is scaled back to be of this length at the beginning of the line search
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-snes_linesearch_max_it <40> </B></TD><TD>- maximum number of shrinking step
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-snes_linesearch_minlambda <1e-12> </B></TD><TD>- minimum step length allowed
</TD></TR>
<TR><TD WIDTH=40></TD><TD ALIGN=LEFT VALIGN=TOP><B>-snes_linesearch_order <cubic,quadratic> </B></TD><TD>- order of the approximation
</TD></TR></TABLE>
<P>
<P>
<H3><FONT COLOR="#CC3333">Notes</FONT></H3>
This line search is taken from "Numerical Methods for Unconstrained
Optimization and Nonlinear Equations" by Dennis and Schnabel, page 325.
<P>
This line search will always produce a step that is less than or equal to, in length, the full step size.
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../SNES/SNESLineSearchCreate.html#SNESLineSearchCreate">SNESLineSearchCreate</A>(), <A HREF="../SNES/SNESLineSearchSetType.html#SNESLineSearchSetType">SNESLineSearchSetType</A>()
<BR><P><B></B><H3><FONT COLOR="#CC3333">Level</FONT></H3>advanced<BR>
<H3><FONT COLOR="#CC3333">Location</FONT></H3>
</B><A HREF="../../../src/snes/linesearch/impls/bt/linesearchbt.c.html#SNESLINESEARCHBT">src/snes/linesearch/impls/bt/linesearchbt.c</A>
<BR><A HREF="./index.html">Index of all SNES routines</A>
<BR><A HREF="../../index.html">Table of Contents for all manual pages</A>
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