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<h3 class="section">26.4 Index Look-up and Acceleration</h3>
<p>The state of searches can be stored in a <code>gsl_interp_accel</code> object,
which is a kind of iterator for interpolation lookups. It caches the
previous value of an index lookup. When the subsequent interpolation
point falls in the same interval its index value can be returned
immediately.
<div class="defun">
— Function: size_t <b>gsl_interp_bsearch</b> (<var>const double x_array</var>[]<var>, double x, size_t index_lo, size_t index_hi</var>)<var><a name="index-gsl_005finterp_005fbsearch-2094"></a></var><br>
<blockquote><p>This function returns the index i of the array <var>x_array</var> such
that <code>x_array[i] <= x < x_array[i+1]</code>. The index is searched for
in the range [<var>index_lo</var>,<var>index_hi</var>]. An inline version of this function is used when <code>HAVE_INLINE</code> is defined.
</p></blockquote></div>
<div class="defun">
— Function: gsl_interp_accel * <b>gsl_interp_accel_alloc</b> (<var>void</var>)<var><a name="index-gsl_005finterp_005faccel_005falloc-2095"></a></var><br>
<blockquote><p>This function returns a pointer to an accelerator object, which is a
kind of iterator for interpolation lookups. It tracks the state of
lookups, thus allowing for application of various acceleration
strategies.
</p></blockquote></div>
<div class="defun">
— Function: size_t <b>gsl_interp_accel_find</b> (<var>gsl_interp_accel * a, const double x_array</var>[]<var>, size_t size, double x</var>)<var><a name="index-gsl_005finterp_005faccel_005ffind-2096"></a></var><br>
<blockquote><p>This function performs a lookup action on the data array <var>x_array</var>
of size <var>size</var>, using the given accelerator <var>a</var>. This is how
lookups are performed during evaluation of an interpolation. The
function returns an index i such that <code>x_array[i] <= x <
x_array[i+1]</code>. An inline version of this function is used when <code>HAVE_INLINE</code> is defined.
</p></blockquote></div>
<div class="defun">
— Function: void <b>gsl_interp_accel_free</b> (<var>gsl_interp_accel* acc</var>)<var><a name="index-gsl_005finterp_005faccel_005ffree-2097"></a></var><br>
<blockquote><p>This function frees the accelerator object <var>acc</var>.
</p></blockquote></div>
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