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<title>X_SOLVE_DC_DRIFT</title>
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<h1 align=center>X_SOLVE_DC_DRIFT</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#BEWARE">BEWARE</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#REFERENCES">REFERENCES</a><br>
<hr>
<a name="NAME"></a>
<h2>NAME</h2>
<p style="margin-left:11%; margin-top: 1em"><b>x_solve_dc_drift</b>
− Find Best-fitting D.C.-shift and Drift Estimates</p>
<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
<p style="margin-left:11%; margin-top: 1em"><b>x_solve_dc_drift</b>
[ <b>−X</b><i>xbase</i> ] [
<b>−L</b><i>lbase</i> ] [
<b>−I</b><i>ignorefile</i> ] [ <b>−S</b> ] [
<b>−C</b><i>iteration</i> ] [
<b>−M</b><i>min_nx</i> ] [
<b>−R</b><i>west/east/south/north</i> ] [
<b>−U</b><i>uselegsfile</i> ] [ <b>−V</b> ] [
<b>−B</b><i>binfile</i> ] [
<b>−A</b><i>ASCIIfile</i> ]</p>
<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
<p style="margin-left:11%; margin-top: 1em"><b>x_solve_dc_drift</b>
will read the database files and, by iterating, find the
best-fitting regression line to the <time,COE> points
for each leg that minimizes the overall standard deviation
of the data set in a least squares sense. Finally,
correction file(s) are created.</p>
<table width="100%" border=0 rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−X</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Indicate an
alternate database to read. [Default is
<i>xx_base.b</i>].</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−L</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Indicate an
alternate legbase to read. [Default is
<i>xx_legs.b</i>].</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−I</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Ignore information
for certain legs (that might be bad, etc).</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−S</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Reset the old
d.c.-shift and drift estimates to zero before iterating.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−C</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Specify how many
iterations to do. Default is interactive session.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−M</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Solve for drift
only if the leg has more than <i>min_nx</i> cross-overs.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−R</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Only take COEs
inside this region into account. [Default is world].</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−U</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Solve for
corrections involving COEs from legs in the
<i>uselegsfile</i> only.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−B</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Create a binary
correction file (which can be read by <b><A HREF="x_list.html">x_list</A></b> and
<b><A HREF="gmtlist.html">gmtlist</A></b>).</p> </td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−A</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Create an ASCII
correction table. At least one of <b>−A</b> and
<b>−B</b> must be specified.</p></td>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="3%">
<p style="margin-top: 1em" valign="top"><b>−V</b></p> </td>
<td width="8%"></td>
<td width="78%">
<p style="margin-top: 1em" valign="top">Selects verbose
mode, which will send progress reports to stderr [Default
runs "silently"].</p></td>
</table>
<a name="BEWARE"></a>
<h2>BEWARE</h2>
<p style="margin-left:11%; margin-top: 1em">The reason for
the <b>−M</b> option is that if the COEs are few, then
a stable estimate of the slope may not be obtained (e.g.
when most of the COEs occur midway between ports). However,
in most cases the bulk of the COEs do occur near the ports
so that a drift estimate can be computed. Conventional
wisdom recommends plotting the time-series and the computed
regression line to see if it makes sense.</p>
<a name="SEE ALSO"></a>
<h2>SEE ALSO</h2>
<p style="margin-left:11%; margin-top: 1em"><i><A HREF="GMT.html">GMT</A></i>(1),
<i><A HREF="x_system.html">x_system</A></i>(1)</p>
<a name="REFERENCES"></a>
<h2>REFERENCES</h2>
<p style="margin-left:11%; margin-top: 1em">Wessel, P.
XOVER: A Cross-over Error Detector for Track Data,
<i>Computers & Geosciences, 15</i>, 333-346.</p>
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