Note that for a hydraulic problem the most convenient selection of the pipe diameters poses additional constraints
on the pressures which should exist in the individual nodes of the network. The PSO algorithm – like all evolutionary
algorithms – cannot directly handle the constraints of the optimization problem. As described in the previous section,
the standard technique to convert the constrained system into a free system uses an appropriate penalty function P
in Eq. (1). To direct the search away from the excluded domains towards the allowed regions, the penalty function
increases correspondingly to exclude any unwanted solutions