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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<h2><span class="refentrytitle"><a name="libgwyddion-GwyExpr.top_of_page"></a>GwyExpr</span></h2>
<p>GwyExpr — Arithmetic expression parser and evaluator</p>
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<div class="refsynopsisdiv">
<a name="libgwyddion-GwyExpr.synopsis"></a><h2>Synopsis</h2>
<pre class="synopsis">
#include &lt;libgwyddion/gwyddion.h&gt;

#define             <a class="link" href="libgwyddion-GwyExpr.html#GWY-EXPR-ERROR:CAPS" title="GWY_EXPR_ERROR">GWY_EXPR_ERROR</a>
                    <a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr">GwyExpr</a>;
enum                <a class="link" href="libgwyddion-GwyExpr.html#GwyExprError" title="enum GwyExprError">GwyExprError</a>;
<a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-compile" title="gwy_expr_compile ()">gwy_expr_compile</a>                    (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code>const <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gchar"><span class="type">gchar</span></a> *text</code></em>,
                                                         <em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Error-Reporting.html#GError"><span class="type">GError</span></a> **err</code></em>);
<a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-define-constant" title="gwy_expr_define_constant ()">gwy_expr_define_constant</a>            (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code>const <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gchar"><span class="type">gchar</span></a> *name</code></em>,
                                                         <em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> value</code></em>,
                                                         <em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Error-Reporting.html#GError"><span class="type">GError</span></a> **err</code></em>);
<a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Quarks.html#GQuark"><span class="returnvalue">GQuark</span></a>              <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-error-quark" title="gwy_expr_error_quark ()">gwy_expr_error_quark</a>                (<em class="parameter"><code><span class="type">void</span></code></em>);
<a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-evaluate" title="gwy_expr_evaluate ()">gwy_expr_evaluate</a>                   (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code>const <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gchar"><span class="type">gchar</span></a> *text</code></em>,
                                                         <em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *result</code></em>,
                                                         <em class="parameter"><code><a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Error-Reporting.html#GError"><span class="type">GError</span></a> **err</code></em>);
<a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="returnvalue">gdouble</span></a>             <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-execute" title="gwy_expr_execute ()">gwy_expr_execute</a>                    (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code>const <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *values</code></em>);
<span class="returnvalue">void</span>                <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-free" title="gwy_expr_free ()">gwy_expr_free</a>                       (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>);
const <a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gchar"><span class="returnvalue">gchar</span></a> *       <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-get-expression" title="gwy_expr_get_expression ()">gwy_expr_get_expression</a>             (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>);
<a href="http://developer.gnome.org/doc/API/2.0/glib/glib-Basic-Types.html#gint"><span class="returnvalue">gint</span></a>                <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-get-variables" title="gwy_expr_get_variables ()">gwy_expr_get_variables</a>              (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gchar"><span class="type">gchar</span></a> ***names</code></em>);
<a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="returnvalue">GwyExpr</span></a> *           <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-new" title="gwy_expr_new ()">gwy_expr_new</a>                        (<em class="parameter"><code><span class="type">void</span></code></em>);
<a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#guint"><span class="returnvalue">guint</span></a>               <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-resolve-variables" title="gwy_expr_resolve_variables ()">gwy_expr_resolve_variables</a>          (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#guint"><span class="type">guint</span></a> n</code></em>,
                                                         <em class="parameter"><code>const <a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gchar"><span class="type">gchar</span></a> * const *names</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#guint"><span class="type">guint</span></a> *indices</code></em>);
<a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-undefine-constant" title="gwy_expr_undefine_constant ()">gwy_expr_undefine_constant</a>          (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code>const <a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gchar"><span class="type">gchar</span></a> *name</code></em>);
<span class="returnvalue">void</span>                <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-vector-execute" title="gwy_expr_vector_execute ()">gwy_expr_vector_execute</a>             (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#guint"><span class="type">guint</span></a> n</code></em>,
                                                         <em class="parameter"><code>const <a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> **data</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *result</code></em>);
</pre>
</div>
<div class="refsect1">
<a name="libgwyddion-GwyExpr.description"></a><h2>Description</h2>
<p>
<a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> is an expression evaluator, more precisely parser, compiler, and
evaluator. A new <a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> can be created with <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-new" title="gwy_expr_new ()"><code class="function">gwy_expr_new()</code></a>, then it can be
used to evaluate any number of expressions; when it's no longer needed, it
should be destroyed with <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-free" title="gwy_expr_free ()"><code class="function">gwy_expr_free()</code></a>.
</p>
<p>
Expression syntax is described in
<a class="ulink" href="http://gwyddion.net/documentation/user-guide/expression-syntax.html" target="_top">Gwyddion user guide</a>.
</p>
<p>
Simple arithmetic expressions without variables can be directly evaluated
with <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-evaluate" title="gwy_expr_evaluate ()"><code class="function">gwy_expr_evaluate()</code></a>.
</p>
<p>
Expression with variables have to be compiled first with <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-compile" title="gwy_expr_compile ()"><code class="function">gwy_expr_compile()</code></a>.
Then either <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-resolve-variables" title="gwy_expr_resolve_variables ()"><code class="function">gwy_expr_resolve_variables()</code></a> or <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-get-variables" title="gwy_expr_get_variables ()"><code class="function">gwy_expr_get_variables()</code></a> can be
used to obtain information what variables are present in the expression and
at which positions (variables are referenced by position, not name during
final evaluation because of effieiency reasons). Subsequent evaluation with
variable substitution is performed by <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-execute" title="gwy_expr_execute ()"><code class="function">gwy_expr_execute()</code></a>. It is also
possible to evaluate expression on each item of value arrays with
<a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-vector-execute" title="gwy_expr_vector_execute ()"><code class="function">gwy_expr_vector_execute()</code></a>.
</p>
<p>
One-shot evaluation of expressions without variables is easy:
</p>
<div class="informalexample">
  <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
    <tbody>
      <tr>
        <td class="listing_lines" align="right"><pre>1
2
3
4
5
6
7
8
9
10</pre></td>
        <td class="listing_code"><pre class="programlisting"><span class="usertype">GwyExpr</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">expr</span><span class="symbol">;</span>
<span class="usertype">GError</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">err </span><span class="symbol">=</span><span class="normal"> <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">;</span>
<span class="usertype">gdouble</span><span class="normal"> result</span><span class="symbol">;</span>

<span class="normal">expr </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="#gwy-expr-new">gwy_expr_new</a></span><span class="symbol">();</span>
<span class="keyword">if</span><span class="normal"> </span><span class="symbol">(!</span><span class="function"><a href="#gwy-expr-evaluate">gwy_expr_evaluate</a></span><span class="symbol">(</span><span class="normal">expr</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"1+2"</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&amp;</span><span class="normal">result</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&amp;</span><span class="normal">err</span><span class="symbol">))</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">    </span><span class="comment">/* Handle compilation error */</span>
<span class="cbracket">}</span>
<span class="function"><a href="/usr/share/gtk-doc/html/glib/glib-Warnings-and-Assertions.html#g-print">g_print</a></span><span class="symbol">(</span><span class="string">"The result: %g</span><span class="specialchar">\n</span><span class="string">"</span><span class="symbol">,</span><span class="normal"> result</span><span class="symbol">);</span>
<span class="function"><a href="#gwy-expr-free">gwy_expr_free</a></span><span class="symbol">(</span><span class="normal">expr</span><span class="symbol">);</span></pre></td>
      </tr>
    </tbody>
  </table>
</div>

<p>
</p>
<p>
One-shot evaluation of expressions with known variables can be performed by
defining them as constants beforehand:
</p>
<div class="informalexample">
  <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
    <tbody>
      <tr>
        <td class="listing_lines" align="right"><pre>1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16</pre></td>
        <td class="listing_code"><pre class="programlisting"><span class="usertype">GwyExpr</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">expr</span><span class="symbol">;</span>
<span class="usertype">GError</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">err </span><span class="symbol">=</span><span class="normal"> <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">;</span>
<span class="usertype">gdouble</span><span class="normal"> result</span><span class="symbol">;</span>

<span class="comment">/* Create expression and define variables as constants */</span>
<span class="normal">expr </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="#gwy-expr-new">gwy_expr_new</a></span><span class="symbol">();</span>
<span class="function"><a href="#gwy-expr-define-constant">gwy_expr_define_constant</a></span><span class="symbol">(</span><span class="normal">expr</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"x"</span><span class="symbol">,</span><span class="normal"> </span><span class="number">3.0</span><span class="symbol">,</span><span class="normal"> <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">);</span>
<span class="function"><a href="#gwy-expr-define-constant">gwy_expr_define_constant</a></span><span class="symbol">(</span><span class="normal">expr</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"y"</span><span class="symbol">,</span><span class="normal"> </span><span class="number">4.0</span><span class="symbol">,</span><span class="normal"> <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">);</span>

<span class="comment">/* Evaluate expression */</span>
<span class="keyword">if</span><span class="normal"> </span><span class="symbol">(!</span><span class="function"><a href="#gwy-expr-evaluate">gwy_expr_evaluate</a></span><span class="symbol">(</span><span class="normal">expr</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"hypot x,y"</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&amp;</span><span class="normal">result</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&amp;</span><span class="normal">err</span><span class="symbol">))</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">    </span><span class="comment">/* Handle compilation error */</span>
<span class="cbracket">}</span>
<span class="function"><a href="/usr/share/gtk-doc/html/glib/glib-Warnings-and-Assertions.html#g-print">g_print</a></span><span class="symbol">(</span><span class="string">"The result: %g</span><span class="specialchar">\n</span><span class="string">"</span><span class="symbol">,</span><span class="normal"> result</span><span class="symbol">);</span>

<span class="function"><a href="#gwy-expr-free">gwy_expr_free</a></span><span class="symbol">(</span><span class="normal">expr</span><span class="symbol">);</span></pre></td>
      </tr>
    </tbody>
  </table>
</div>

<p>
</p>
<p>
When the same expression is evaluated multiple times with different
variable values and the variables are again from some known set, the
<a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-resolve-variables" title="gwy_expr_resolve_variables ()"><code class="function">gwy_expr_resolve_variables()</code></a> should be used (if the repeated evaluation
happens over items of some arrays, <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-vector-execute" title="gwy_expr_vector_execute ()"><code class="function">gwy_expr_vector_execute()</code></a> is more
efficient and usually simplier to use too):
</p>
<div class="informalexample">
  <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
    <tbody>
      <tr>
        <td class="listing_lines" align="right"><pre>1
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        <td class="listing_code"><pre class="programlisting"><span class="usertype">GwyExpr</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">expr</span><span class="symbol">;</span>
<span class="usertype">GError</span><span class="normal"> </span><span class="symbol">*</span><span class="normal">err </span><span class="symbol">=</span><span class="normal"> <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">;</span>
<span class="keyword">const</span><span class="normal"> <a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gchar">gchar</a> </span><span class="symbol">*</span><span class="keyword">const</span><span class="normal"> var_names</span><span class="symbol">[]</span><span class="normal"> </span><span class="symbol">=</span><span class="normal"> </span><span class="cbracket">{</span><span class="normal"> </span><span class="string">"lambda"</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"theta"</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"psi"</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"d"</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"k"</span><span class="normal"> </span><span class="cbracket">}</span><span class="symbol">;</span>
<span class="keyword">const</span><span class="normal"> </span><span class="usertype">gdouble</span><span class="normal"> var_values1</span><span class="symbol">[]</span><span class="normal"> </span><span class="symbol">=</span><span class="normal"> </span><span class="cbracket">{</span><span class="normal"> </span><span class="number">300.0</span><span class="symbol">,</span><span class="normal"> </span><span class="number">0.09</span><span class="symbol">,</span><span class="normal"> </span><span class="number">2.0</span><span class="symbol">,</span><span class="normal"> </span><span class="number">52.3</span><span class="symbol">,</span><span class="normal"> </span><span class="number">1.43</span><span class="normal"> </span><span class="cbracket">}</span><span class="symbol">;</span>
<span class="keyword">const</span><span class="normal"> </span><span class="usertype">gdouble</span><span class="normal"> var_values2</span><span class="symbol">[]</span><span class="normal"> </span><span class="symbol">=</span><span class="normal"> </span><span class="cbracket">{</span><span class="normal"> </span><span class="number">400.0</span><span class="symbol">,</span><span class="normal"> </span><span class="number">0.12</span><span class="symbol">,</span><span class="normal"> </span><span class="number">2.0</span><span class="symbol">,</span><span class="normal"> </span><span class="number">54.1</span><span class="symbol">,</span><span class="normal"> </span><span class="number">1.44</span><span class="normal"> </span><span class="cbracket">}</span><span class="symbol">;</span>
<span class="usertype">guint</span><span class="normal"> var_positions</span><span class="symbol">[</span><span class="function"><a href="/usr/share/gtk-doc/html/glib/glib-Miscellaneous-Macros.html#G-N-ELEMENTS:CAPS">G_N_ELEMENTS</a></span><span class="symbol">(</span><span class="normal">var_names</span><span class="symbol">)];</span>
<span class="usertype">gdouble</span><span class="normal"> vars</span><span class="symbol">[</span><span class="function"><a href="/usr/share/gtk-doc/html/glib/glib-Miscellaneous-Macros.html#G-N-ELEMENTS:CAPS">G_N_ELEMENTS</a></span><span class="symbol">(</span><span class="normal">var_names</span><span class="symbol">)</span><span class="normal"> </span><span class="symbol">+</span><span class="normal"> </span><span class="number">1</span><span class="symbol">];</span>
<span class="usertype">guint</span><span class="normal"> i</span><span class="symbol">;</span>

<span class="comment">/* Create expression and define constant pi */</span>
<span class="normal">expr </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="#gwy-expr-new">gwy_expr_new</a></span><span class="symbol">();</span>
<span class="function"><a href="#gwy-expr-define-constant">gwy_expr_define_constant</a></span><span class="symbol">(</span><span class="normal">expr</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"pi"</span><span class="symbol">,</span><span class="normal"> <a href="/usr/share/gtk-doc/html/glib/glib-Numerical-Definitions.html#G-PI:CAPS">G_PI</a></span><span class="symbol">,</span><span class="normal"> <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">);</span>

<span class="comment">/* Compile expression */</span>
<span class="keyword">if</span><span class="normal"> </span><span class="symbol">(!</span><span class="function"><a href="#gwy-expr-compile">gwy_expr_compile</a></span><span class="symbol">(</span><span class="normal">expr</span><span class="symbol">,</span><span class="normal"> </span><span class="string">"2*pi/lambda*d*sin theta"</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&amp;</span><span class="normal">err</span><span class="symbol">))</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">    </span><span class="comment">/* Handle compilation error */</span>
<span class="cbracket">}</span>

<span class="comment">/* Resolve variables */</span>
<span class="keyword">if</span><span class="normal"> </span><span class="symbol">(</span><span class="function"><a href="#gwy-expr-resolve-variables">gwy_expr_resolve_variables</a></span><span class="symbol">(</span><span class="normal">expr</span><span class="symbol">,</span><span class="normal"> </span><span class="function"><a href="/usr/share/gtk-doc/html/glib/glib-Miscellaneous-Macros.html#G-N-ELEMENTS:CAPS">G_N_ELEMENTS</a></span><span class="symbol">(</span><span class="normal">var_names</span><span class="symbol">),</span>
<span class="normal">                               var_names</span><span class="symbol">,</span><span class="normal"> var_positions</span><span class="symbol">))</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">    </span><span class="comment">/* Expression contains unknown variables */</span>
<span class="cbracket">}</span>

<span class="comment">/* Evaluate first set */</span>
<span class="keyword">for</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">i </span><span class="symbol">=</span><span class="normal"> </span><span class="number">0</span><span class="symbol">;</span><span class="normal"> i </span><span class="symbol">&lt;</span><span class="normal"> </span><span class="function"><a href="/usr/share/gtk-doc/html/glib/glib-Miscellaneous-Macros.html#G-N-ELEMENTS:CAPS">G_N_ELEMENTS</a></span><span class="symbol">(</span><span class="normal">var_names</span><span class="symbol">);</span><span class="normal"> i</span><span class="symbol">++)</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">    vars</span><span class="symbol">[</span><span class="normal">var_positions</span><span class="symbol">[</span><span class="normal">i</span><span class="symbol">]]</span><span class="normal"> </span><span class="symbol">=</span><span class="normal"> var_values1</span><span class="symbol">[</span><span class="normal">i</span><span class="symbol">];</span>
<span class="cbracket">}</span>
<span class="function"><a href="/usr/share/gtk-doc/html/glib/glib-Warnings-and-Assertions.html#g-print">g_print</a></span><span class="symbol">(</span><span class="string">"First result: %g</span><span class="specialchar">\n</span><span class="string">"</span><span class="symbol">,</span><span class="normal"> </span><span class="function"><a href="#gwy-expr-execute">gwy_expr_execute</a></span><span class="symbol">(</span><span class="normal">expr</span><span class="symbol">,</span><span class="normal"> vars</span><span class="symbol">));</span>

<span class="comment">/* Evaluate second set */</span>
<span class="keyword">for</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">i </span><span class="symbol">=</span><span class="normal"> </span><span class="number">0</span><span class="symbol">;</span><span class="normal"> i </span><span class="symbol">&lt;</span><span class="normal"> </span><span class="function"><a href="/usr/share/gtk-doc/html/glib/glib-Miscellaneous-Macros.html#G-N-ELEMENTS:CAPS">G_N_ELEMENTS</a></span><span class="symbol">(</span><span class="normal">var_names</span><span class="symbol">);</span><span class="normal"> i</span><span class="symbol">++)</span>
<span class="normal">    vars</span><span class="symbol">[</span><span class="normal">var_positions</span><span class="symbol">[</span><span class="normal">i</span><span class="symbol">]]</span><span class="normal"> </span><span class="symbol">=</span><span class="normal"> var_values2</span><span class="symbol">[</span><span class="normal">i</span><span class="symbol">];</span>
<span class="function"><a href="/usr/share/gtk-doc/html/glib/glib-Warnings-and-Assertions.html#g-print">g_print</a></span><span class="symbol">(</span><span class="string">"Second result: %g</span><span class="specialchar">\n</span><span class="string">"</span><span class="symbol">,</span><span class="normal"> </span><span class="function"><a href="#gwy-expr-execute">gwy_expr_execute</a></span><span class="symbol">(</span><span class="normal">expr</span><span class="symbol">,</span><span class="normal"> vars</span><span class="symbol">));</span>

<span class="function"><a href="#gwy-expr-free">gwy_expr_free</a></span><span class="symbol">(</span><span class="normal">expr</span><span class="symbol">);</span></pre></td>
      </tr>
    </tbody>
  </table>
</div>

<p>
</p>
<p>
The most general case is when the variables are from a large set (or
completely arbitrary).  Then it is best to get the list of variables with
<a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-get-variables" title="gwy_expr_get_variables ()"><code class="function">gwy_expr_get_variables()</code></a> and supply only values of variables that
are actually present in the expression.
</p>
</div>
<div class="refsect1">
<a name="libgwyddion-GwyExpr.details"></a><h2>Details</h2>
<div class="refsect2">
<a name="GWY-EXPR-ERROR:CAPS"></a><h3>GWY_EXPR_ERROR</h3>
<pre class="programlisting">#define GWY_EXPR_ERROR gwy_expr_error_quark()
</pre>
<p>
Error domain for expression parsing and evaluation. Errors in this domain
will be from the <a class="link" href="libgwyddion-GwyExpr.html#GwyExprError" title="enum GwyExprError"><span class="type">GwyExprError</span></a> enumeration. See <a href="/usr/share/gtk-doc/html/glib/glib-Error-Reporting.html#GError"><span class="type">GError</span></a> for information on
error domains.
</p>
</div>
<hr>
<div class="refsect2">
<a name="GwyExpr"></a><h3>GwyExpr</h3>
<pre class="programlisting">typedef struct _GwyExpr GwyExpr;</pre>
<p>
<a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> is an opaque data structure and should be only manipulated with the
functions below.
</p>
</div>
<hr>
<div class="refsect2">
<a name="GwyExprError"></a><h3>enum GwyExprError</h3>
<pre class="programlisting">typedef enum {
    GWY_EXPR_ERROR_CLOSING_PARENTHESIS,
    GWY_EXPR_ERROR_EMPTY,
    GWY_EXPR_ERROR_EMPTY_PARENTHESES,
    GWY_EXPR_ERROR_GARBAGE,
    GWY_EXPR_ERROR_INVALID_ARGUMENT,
    GWY_EXPR_ERROR_INVALID_TOKEN,
    GWY_EXPR_ERROR_MISSING_ARGUMENT,
    GWY_EXPR_ERROR_NOT_EXECUTABLE,
    GWY_EXPR_ERROR_OPENING_PARENTHESIS,
    GWY_EXPR_ERROR_STRAY_COMMA,
    GWY_EXPR_ERROR_UNRESOLVED_IDENTIFIERS,
    GWY_EXPR_ERROR_CONSTANT_NAME
} GwyExprError;
</pre>
<p>
Error codes returned by expression parsing and execution.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><a name="GWY-EXPR-ERROR-CLOSING-PARENTHESIS:CAPS"></a><span class="term"><code class="literal">GWY_EXPR_ERROR_CLOSING_PARENTHESIS</code></span></p></td>
<td>A closing parenthesis is missing.
</td>
</tr>
<tr>
<td><p><a name="GWY-EXPR-ERROR-EMPTY:CAPS"></a><span class="term"><code class="literal">GWY_EXPR_ERROR_EMPTY</code></span></p></td>
<td>Expression is empty.
</td>
</tr>
<tr>
<td><p><a name="GWY-EXPR-ERROR-EMPTY-PARENTHESES:CAPS"></a><span class="term"><code class="literal">GWY_EXPR_ERROR_EMPTY_PARENTHESES</code></span></p></td>
<td>A parentheses pair contain nothing
                                   inside.
</td>
</tr>
<tr>
<td><p><a name="GWY-EXPR-ERROR-GARBAGE:CAPS"></a><span class="term"><code class="literal">GWY_EXPR_ERROR_GARBAGE</code></span></p></td>
<td>An symbol unexpectedly managed to survive.
</td>
</tr>
<tr>
<td><p><a name="GWY-EXPR-ERROR-INVALID-ARGUMENT:CAPS"></a><span class="term"><code class="literal">GWY_EXPR_ERROR_INVALID_ARGUMENT</code></span></p></td>
<td>Function or operator argument is not a
                                  value.
</td>
</tr>
<tr>
<td><p><a name="GWY-EXPR-ERROR-INVALID-TOKEN:CAPS"></a><span class="term"><code class="literal">GWY_EXPR_ERROR_INVALID_TOKEN</code></span></p></td>
<td>Expression contains an invalid token.
</td>
</tr>
<tr>
<td><p><a name="GWY-EXPR-ERROR-MISSING-ARGUMENT:CAPS"></a><span class="term"><code class="literal">GWY_EXPR_ERROR_MISSING_ARGUMENT</code></span></p></td>
<td>Function or operator arguments is missing.
</td>
</tr>
<tr>
<td><p><a name="GWY-EXPR-ERROR-NOT-EXECUTABLE:CAPS"></a><span class="term"><code class="literal">GWY_EXPR_ERROR_NOT_EXECUTABLE</code></span></p></td>
<td>Compiled stack is not executable.
</td>
</tr>
<tr>
<td><p><a name="GWY-EXPR-ERROR-OPENING-PARENTHESIS:CAPS"></a><span class="term"><code class="literal">GWY_EXPR_ERROR_OPENING_PARENTHESIS</code></span></p></td>
<td>An opening parenthesis is missing.
</td>
</tr>
<tr>
<td><p><a name="GWY-EXPR-ERROR-STRAY-COMMA:CAPS"></a><span class="term"><code class="literal">GWY_EXPR_ERROR_STRAY_COMMA</code></span></p></td>
<td>A comma at the start or end of list.
</td>
</tr>
<tr>
<td><p><a name="GWY-EXPR-ERROR-UNRESOLVED-IDENTIFIERS:CAPS"></a><span class="term"><code class="literal">GWY_EXPR_ERROR_UNRESOLVED_IDENTIFIERS</code></span></p></td>
<td>Expression contains unresolved
                                        identifiers.
</td>
</tr>
<tr>
<td><p><a name="GWY-EXPR-ERROR-CONSTANT-NAME:CAPS"></a><span class="term"><code class="literal">GWY_EXPR_ERROR_CONSTANT_NAME</code></span></p></td>
<td>Constant name is invalid.
</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-expr-compile"></a><h3>gwy_expr_compile ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            gwy_expr_compile                    (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code>const <a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gchar"><span class="type">gchar</span></a> *text</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Error-Reporting.html#GError"><span class="type">GError</span></a> **err</code></em>);</pre>
<p>
Compiles an expression for later execution.
</p>
<p>
This function is useful for expressions with variables.  For normal
arithmetic expressions it's easier to use <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-evaluate" title="gwy_expr_evaluate ()"><code class="function">gwy_expr_evaluate()</code></a>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>expr</code></em> :</span></p></td>
<td>An expression evaluator.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>text</code></em> :</span></p></td>
<td>String containing the expression to compile.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>err</code></em> :</span></p></td>
<td>Location to store compilation or evaluation error to, or <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>.
Errors from <a class="link" href="libgwyddion-GwyExpr.html#GwyExprError" title="enum GwyExprError"><span class="type">GwyExprError</span></a> domain can occur.</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>
<a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a> on success, <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a> if compilation failed.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-expr-define-constant"></a><h3>gwy_expr_define_constant ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            gwy_expr_define_constant            (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code>const <a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gchar"><span class="type">gchar</span></a> *name</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> value</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Error-Reporting.html#GError"><span class="type">GError</span></a> **err</code></em>);</pre>
<p>
Defines a symbolic constant.
</p>
<p>
Note the definition does not affect already compiled expression, you have
to recompile it (and eventually re-resolve variables).
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>expr</code></em> :</span></p></td>
<td>An expression evaluator.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>name</code></em> :</span></p></td>
<td>Name of constant to define.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>value</code></em> :</span></p></td>
<td>Constant numeric value.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>err</code></em> :</span></p></td>
<td>Location to store error to, or <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>.
Only <a class="link" href="libgwyddion-GwyExpr.html#GWY-EXPR-ERROR-CONSTANT-NAME:CAPS"><code class="literal">GWY_EXPR_ERROR_CONSTANT_NAME</code></a> error from <a class="link" href="libgwyddion-GwyExpr.html#GwyExprError" title="enum GwyExprError"><span class="type">GwyExprError</span></a> domain can
occur.</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>
<a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a> on success, <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a> if definition failed.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-expr-error-quark"></a><h3>gwy_expr_error_quark ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Quarks.html#GQuark"><span class="returnvalue">GQuark</span></a>              gwy_expr_error_quark                (<em class="parameter"><code><span class="type">void</span></code></em>);</pre>
<p>
Returns error domain for expression parsin and evaluation.
</p>
<p>
See and use <a class="link" href="libgwyddion-GwyExpr.html#GWY-EXPR-ERROR:CAPS" title="GWY_EXPR_ERROR"><code class="literal">GWY_EXPR_ERROR</code></a>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>The error domain.</td>
</tr></tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-expr-evaluate"></a><h3>gwy_expr_evaluate ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            gwy_expr_evaluate                   (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code>const <a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gchar"><span class="type">gchar</span></a> *text</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *result</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Error-Reporting.html#GError"><span class="type">GError</span></a> **err</code></em>);</pre>
<p>
Evaulates an arithmetic expression.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>expr</code></em> :</span></p></td>
<td>An expression evaluator.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>text</code></em> :</span></p></td>
<td>String containing the expression to evaluate.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>result</code></em> :</span></p></td>
<td>Location to store result to.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>err</code></em> :</span></p></td>
<td>Location to store compilation or evaluation error to, or <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>.
Errors from <a class="link" href="libgwyddion-GwyExpr.html#GwyExprError" title="enum GwyExprError"><span class="type">GwyExprError</span></a> domain can occur.</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>
<a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a> on success, <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a> if evaluation failed.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-expr-execute"></a><h3>gwy_expr_execute ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gdouble"><span class="returnvalue">gdouble</span></a>             gwy_expr_execute                    (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code>const <a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *values</code></em>);</pre>
<p>
Executes a compiled expression with variables, substituting given values.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>expr</code></em> :</span></p></td>
<td>An expression evaluator.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>values</code></em> :</span></p></td>
<td>Array with variable values.  Its zeroth item is always unused.
Variable list can be obtained by <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-get-variables" title="gwy_expr_get_variables ()"><code class="function">gwy_expr_get_variables()</code></a>.</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>The result.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-expr-free"></a><h3>gwy_expr_free ()</h3>
<pre class="programlisting"><span class="returnvalue">void</span>                gwy_expr_free                       (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>);</pre>
<p>
Frees all memory used by an expression evaluator.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td><p><span class="term"><em class="parameter"><code>expr</code></em> :</span></p></td>
<td>An expression evaluator.</td>
</tr></tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-expr-get-expression"></a><h3>gwy_expr_get_expression ()</h3>
<pre class="programlisting">const <a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gchar"><span class="returnvalue">gchar</span></a> *       gwy_expr_get_expression             (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>);</pre>
<p>
Gets the expression string.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>expr</code></em> :</span></p></td>
<td>An expression evaluator.</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>The last string passed to <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-evaluate" title="gwy_expr_evaluate ()"><code class="function">gwy_expr_evaluate()</code></a> or
<a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-compile" title="gwy_expr_compile ()"><code class="function">gwy_expr_compile()</code></a>.  It is owned by <em class="parameter"><code>expr</code></em> and must not be modified
or freed.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-expr-get-variables"></a><h3>gwy_expr_get_variables ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gint"><span class="returnvalue">gint</span></a>                gwy_expr_get_variables              (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gchar"><span class="type">gchar</span></a> ***names</code></em>);</pre>
<p>
Get the number, names, and indices of unresolved identifiers in <em class="parameter"><code>expr</code></em>.
</p>
<p>
It is an error to call this function after an unsuccessful compilation.
</p>
<p>
If you only care about variables from a prefedined set, that is if any
unknown variable is an error, it's easier to use
<a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-resolve-variables" title="gwy_expr_resolve_variables ()"><code class="function">gwy_expr_resolve_variables()</code></a>.
</p>
<p>
The position of each variable in <em class="parameter"><code>names</code></em> corresponds to the position of its
value in <em class="parameter"><code>values</code></em> array in <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-execute" title="gwy_expr_execute ()"><code class="function">gwy_expr_execute()</code></a> call.  Namely, the first item
in the array is always reserved and do not correspond to any variable.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>expr</code></em> :</span></p></td>
<td>An expression evaluator.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>names</code></em> :</span></p></td>
<td>Location to store pointer to array of variable names to (may be
<a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a> to get just number of variables).  The string array returned
in this argument in owned by <em class="parameter"><code>expr</code></em> and is valid only until next
<a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-compile" title="gwy_expr_compile ()"><code class="function">gwy_expr_compile()</code></a>, <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-evaluate" title="gwy_expr_evaluate ()"><code class="function">gwy_expr_evaluate()</code></a>, or <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-free" title="gwy_expr_free ()"><code class="function">gwy_expr_free()</code></a>
call.</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>The length of array stored to <em class="parameter"><code>names</code></em>.  This is the number of
variables plus one (for the first reserved item).
On failure, 0 is returned.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-expr-new"></a><h3>gwy_expr_new ()</h3>
<pre class="programlisting"><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="returnvalue">GwyExpr</span></a> *           gwy_expr_new                        (<em class="parameter"><code><span class="type">void</span></code></em>);</pre>
<p>
Creates a new expression evaluator.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>A newly created expression evaluator.</td>
</tr></tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-expr-resolve-variables"></a><h3>gwy_expr_resolve_variables ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#guint"><span class="returnvalue">guint</span></a>               gwy_expr_resolve_variables          (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#guint"><span class="type">guint</span></a> n</code></em>,
                                                         <em class="parameter"><code>const <a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gchar"><span class="type">gchar</span></a> * const *names</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#guint"><span class="type">guint</span></a> *indices</code></em>);</pre>
<p>
Finds positions of variables in an expression.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>expr</code></em> :</span></p></td>
<td>An expression evaluator.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>n</code></em> :</span></p></td>
<td>The length of <em class="parameter"><code>names</code></em> and <em class="parameter"><code>indices</code></em> arrays.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>names</code></em> :</span></p></td>
<td>List of variable names to get positions of.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>indices</code></em> :</span></p></td>
<td>Array to store variable positions to.  The positions are the same
as in <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-execute" title="gwy_expr_execute ()"><code class="function">gwy_expr_execute()</code></a>.  Variables not present in the expression
are assigned (reserved) position 0.  This allows to safely
substitute values of all variables before execution wthout caring
which variables are actually present.</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>The number of remaining, unresolved variables in <em class="parameter"><code>expr</code></em>.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-expr-undefine-constant"></a><h3>gwy_expr_undefine_constant ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>            gwy_expr_undefine_constant          (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code>const <a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gchar"><span class="type">gchar</span></a> *name</code></em>);</pre>
<p>
Undefines a symbolic constant.
</p>
<p>
Note the definition removal does not affect already compiled expression,
you have to recompile it (and eventually re-resolve variables).
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>expr</code></em> :</span></p></td>
<td>An expression evaluator.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>name</code></em> :</span></p></td>
<td>Name of constant to undefine.</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>
<a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#TRUE:CAPS"><code class="literal">TRUE</code></a> if there was such a constant and was removed, <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#FALSE:CAPS"><code class="literal">FALSE</code></a>
otherwise.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="gwy-expr-vector-execute"></a><h3>gwy_expr_vector_execute ()</h3>
<pre class="programlisting"><span class="returnvalue">void</span>                gwy_expr_vector_execute             (<em class="parameter"><code><a class="link" href="libgwyddion-GwyExpr.html#GwyExpr" title="GwyExpr"><span class="type">GwyExpr</span></a> *expr</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#guint"><span class="type">guint</span></a> n</code></em>,
                                                         <em class="parameter"><code>const <a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> **data</code></em>,
                                                         <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gdouble"><span class="type">gdouble</span></a> *result</code></em>);</pre>
<p>
Executes a compiled expression on each item of data arrays.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>expr</code></em> :</span></p></td>
<td>An expression evaluator.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>n</code></em> :</span></p></td>
<td>The lenght of <em class="parameter"><code>result</code></em> and of <em class="parameter"><code>data</code></em> member arrays, that is vector length.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>data</code></em> :</span></p></td>
<td>An array of arrays of length <em class="parameter"><code>n</code></em>.  The arrays correspond to expression
variables in <a class="link" href="libgwyddion-GwyExpr.html#gwy-expr-execute" title="gwy_expr_execute ()"><code class="function">gwy_expr_execute()</code></a>.  Zeroth array can be <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>.</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>result</code></em> :</span></p></td>
<td>An array of length <em class="parameter"><code>n</code></em> to store computation results to.  It may be
one of those in <em class="parameter"><code>data</code></em>.</td>
</tr>
</tbody>
</table></div>
</div>
</div>
</div>
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