-sum Function</h3>
<p>The higher-order reduce function takes a partial sum function <code>f</code>, an array argument <code>x</code> (with one array element for each term in the sum), a recommended <code>grainsize</code>, and a set of shared arguments. This representation allows parallelization of the resultant sum.</p>
<!-- real; reduce_sum; (F f, T[] x, int grainsize, T1 s1, T2 s2, ...); -->

<p><code>real</code> <strong><code>reduce_sum</code></strong><code>(F f, T[] x, int grainsize, T1 s1, T2 s2, ...)<