A Layer may contain any number of instances of class ParticleLayout.
If a layer has more than one layout, then their scattering intensities add incoherently.
To create a particle layout and add kinds of particles, use
layout = ba.ParticleLayout()
layout.addParticle(particle, abundance)
For the particle argument, see Particle.
If the abundance argument is omitted, then the abundance will be taken from the
particle, which by default has an abundance of 1.
If there is one single kind of particles, then the addParticle call
can be replaced by a constructor call with particle argument:
layout = ba.ParticleLayout(particle)
To set an inter-particle structure, use
layout.setInterference(interparticle)
For the argument, see Particle assemblies.
To set the total particle surface density (in units of nm$^{-2}$), use
layout.setTotalParticleSurfaceDensity(particle_density)