Motivation
For an imported medium described by smoothed particles, when calculating the medium property values in each spatial grid cell during setup, medium properties other than the medium density were taken from the particle nearest the sample location, rather than interpolating over all overlapping particles. Moreover, in rare cases, the code would use a particle close to the sample location but not the nearest particle.

Description
With this new version, medium properties are sampled from an imported particle medium as follows:

• density is properly interpolated over all overlapping particles, as before.
• metallicity, temperature, bulk velocity, and magnetic field are now also properly interpolated over all overlapping particles using density-weighted averaging.
• any additional parameters requested by a material mix or used for selecting a variable material mix are taken from the particle with the highest mass density at the sample location; this is because it is unknown a priori if and how these parameters should be averaged for interpolation.

Tests
All functional tests work. Those affected by the change were adjusted.