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<span id="Function-parcellfun"></span><h3 class="section">2.1 Function parcellfun</h3>
<span id="index-parcellfun-6"></span>
<span id="XREFparcellfun"></span><dl>
<dt id="index-parcellfun">Function File: <em>[<var>o1</var>, <var>o2</var>, …] =</em> <strong>parcellfun</strong> <em>(<var>nproc</var>, <var>fun</var>, <var>a1</var>, <var>a2</var>, …)</em></dt>
<dt id="index-parcellfun-1">Function File: <em></em> <strong>parcellfun</strong> <em>(nproc, fun, …, "UniformOutput", <var>val</var>)</em></dt>
<dt id="index-parcellfun-2">Function File: <em></em> <strong>parcellfun</strong> <em>(nproc, fun, …, "ErrorHandler", <var>errfunc</var>)</em></dt>
<dt id="index-parcellfun-3">Function File: <em></em> <strong>parcellfun</strong> <em>(nproc, fun, …, "VerboseLevel", <var>val</var>)</em></dt>
<dt id="index-parcellfun-4">Function File: <em></em> <strong>parcellfun</strong> <em>(nproc, fun, …, "ChunksPerProc", <var>val</var>)</em></dt>
<dt id="index-parcellfun-5">Function File: <em></em> <strong>parcellfun</strong> <em>(nproc, fun, …, "CumFunc", <var>cumfunc</var>)</em></dt>
<dd><p>Evaluates a function for multiple argument sets using multiple
processes in parallel.
</p>
<p><var>nproc</var> specifies the number of processes and must be at least
1. It will be cut to the number of available CPU cores or the size
of the input argument(s), whichever is lower. <var>fun</var> is a
function handle pointing to the requested evaluating
function. <var>a1</var>, <var>a2</var> etc. should be cell arrays of equal
size. <var>o1</var>, <var>o2</var> etc. will be set to corresponding output
arguments.
</p>
<p>The UniformOutput and ErrorHandler options are supported with
meaning identical to <em>cellfun</em>. If option VerboseLevel is set
to 1 (default is 0), progress messages are printed to stderr. The
ChunksPerProc option controls the number of chunks which contains
elementary jobs. This option is particularly useful when time
execution of function is small. Setting this option to 100 is a
good choice in most cases.
</p>
<p>Instead of returning a result for each argument, parcellfun returns
only one cumulative result if "CumFunc" is non-empty. <var>cumfunc</var>
must be a function which performs an operation on two sets of
outputs of <var>fun</var> and returnes as many outputs as <var>fun</var>. If
<var>nout</var> is the number of outputs of <var>fun</var>, <var>cumfunc</var>
gets a previous output set of <var>fun</var> or of <var>cumfunc</var> as
first <var>nout</var> arguments and the current output of <var>fun</var> as
last <var>nout</var> arguments. The performed operation must be
mathematically commutative and associative. If the operation is
e.g. addition, the result will be the sum(s) of the outputs of
<var>fun</var> over all calls of <var>fun</var>. Since floating point
addition and multiplication are only approximately associative, the
cumulative result will not be exactly reproducible.
</p>
<p>Each process has its own pseudo random number generator, so when
using this function for example to perform Monte-Carlo simulations
one generally cannot expect results to be exactly
reproducible. Exact reproducibility may be achievable by generating
the random number sequence before calling parcellfun and providing
the random numbers as arguments to <var>fun</var>.
</p>
<p>See <code>parallel_doc ("limitations")</code> for possible limitations on
how <var>fun</var> can be defined.
</p>
<p><strong>See also:</strong> <a href="parcellfun_005fset_005fnproc.html#XREFparcellfun_005fset_005fnproc">parcellfun_set_nproc</a>.
</p></dd></dl>
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