Editing Parallel Computing (section)

===Parallel Flow() using split and reduce===
The split option specifies the number of the axis to be split and the size of that axis. For an axis 3 of length 1000 on the standard in file, and collection by concatenation:
<syntaxhighlight lang="python">
Flow('radon','spike','radon adj=y p0=-4 np=200 dp=0.04',split=[3,1000],reduce='cat')
</syntaxhighlight>
Concatenation on the same axis as specified by <tt>split=</tt> is the default reduction method. Possible other valid options are <tt>reduce='add'</tt>, <tt>reduce='cat axis=1'</tt>, etc. Examples can be found in [http://www.ahay.org/RSF/book/rsf/school/data.html $RSFSRC/book/rsf/school/data/SConstruct] and $RSFSRC/book/trip/pscons/SConstruct.

If flows that are run by <tt>pscons</tt> contain both serial and parallel targets, care must be exercised in order to not create bottlenecks, in which tasks are distributed to multiple nodes, but the nodes sit idle while waiting for other nodes to finish computing dependencies. Tasks that are not explicitly parallelized will be sped up by <tt>pscons</tt> if they are independent from each other. For example, compiling Madagascar itself with <tt>pscons</tt> instead of scons results in a visible speedup on a multithreaded machine.