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<?xml version="1.0" encoding="UTF-8"?>
<refentry xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:svg="http://www.w3.org/2000/svg" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:db="http://docbook.org/ns/docbook" version="5.0-subset Scilab" xml:lang="en" xml:id="external">
<info>
<pubdate>$LastChangedDate$</pubdate>
</info>
<refnamediv>
<refname>external</refname>
<refpurpose> Scilab Object, external function or routine</refpurpose>
</refnamediv>
<refsection>
<title>Description</title>
<para>
External function or routine for use with specific commands.</para>
<para>
An "external" is a function or routine which is used as an argument
of some high-level primitives (such as <literal>ode</literal>, <literal>optim</literal>, <literal>schur</literal>...).</para>
<para>
The calling sequence of the external (function or routine) is imposed by
the high-level primitive which sets the arguments of the external.</para>
<para>
For example the external function <literal>costfunc</literal> is an argument of the <literal>optim</literal>
primitive. Its calling sequence must be: <literal>[f,g,ind]=costfunc(x,ind)</literal> and
<literal>optim</literal> (the high-level optimization primitive) is invoked as follows:</para>
<programlisting role = ""><![CDATA[
optim(costfunc,...)
]]></programlisting>
<para>
Here <literal>costfunc</literal> (the cost function to be minimized by the primitive <literal>optim</literal>)
evaluates <literal>f=f(x)</literal> and <literal>g=</literal> gradient of <literal>f</literal> at <literal>x</literal> (<literal>ind</literal> is an integer. Its use is precised in the <literal>optim</literal> help).</para>
<para>
If other values are needed by the external function these variables
can be defined in its environment. Also, they can be put in a list.
For example,the external function</para>
<programlisting role = ""><![CDATA[
[f,g,ind]=costfunc(x,ind,a,b,c)
]]></programlisting>
<para>
is valid for <literal>optim</literal> if the external is <literal>list(costfunc,a,b,c)</literal> and
the call to <literal>optim</literal> is then:</para>
<programlisting role = ""><![CDATA[
optim(list(costfunc,a1,b1,c1),....
]]></programlisting>
<para>
An external can also be a Fortran or C routine : this is convenient to speed up
the computations.</para>
<para>
The name of the routine is given to the high-level primitive
as a character string. The calling sequence of the routine
is also imposed.
</para>
<para>
External Fortran or C routines can also be dynamically linked (see <literal>link</literal>)</para>
</refsection>
<refsection>
<title>See Also</title>
<simplelist type="inline">
<member>
<link linkend="ode">ode</link>
</member>
<member>
<link linkend="optim">optim</link>
</member>
<member>
<link linkend="impl">impl</link>
</member>
<member>
<link linkend="dassl">dassl</link>
</member>
<member>
<link linkend="intg">intg</link>
</member>
<member>
<link linkend="schur">schur</link>
</member>
<member>
<link linkend="gschur">gschur</link>
</member>
</simplelist>
</refsection>
</refentry>
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