Merge pull request #11 from NQCD/velocity-com

VelocityBoltzmann with centre of mass shift

src/nuclear/boltzmann.jl

@@ -1,16 +1,17 @@
 
 """
-    VelocityBoltzmann(temperature, masses::AbstractVector, dims::Dims{2})
+    VelocityBoltzmann(temperature, masses::AbstractVector, dims::Dims{2};  centre = nothing)
 
-Generate a Boltzmann of velocities for each degree of freedom.
+Generate a Boltzmann distribution of velocities for each degree of freedom.
 
 # Arguments
 
 * `temperature` - Atomic units or Unitful
 * `masses` - Vector of masses for each atom
 * `dims` - (ndofs, natoms). `natoms` must equal `length(masses)`
+* `centre` - Vector of dimension ndofs that provides centre of mass velocity offset
 """
-function VelocityBoltzmann(temperature, masses::AbstractVector, dims::Dims{2})
-    return UnivariateArray([VelocityBoltzmann(temperature, masses[I[2]]) for I in CartesianIndices(dims)])
+function VelocityBoltzmann(temperature, masses::AbstractVector, dims::Dims{2};  centre = zeros(dims))
+    return UnivariateArray([VelocityBoltzmann(temperature, masses[I[2]]; centre = centre[I]) for I in CartesianIndices(dims)])
 end
-VelocityBoltzmann(temperature, mass) = Normal(0, sqrt(austrip(temperature)/mass))
+VelocityBoltzmann(temperature, mass; centre = 0) = Normal(centre, sqrt(austrip(temperature)/mass))