# Density field interpolation

Sometimes we have a density field and we would like to evalute it at some positions (e.g. particle positions, void positions…etc). Pylians provides the routine `CIC_interp`

to accomplish this. That routine uses the Cloud-in-Cell (CIC) scheme to interpolate the density field into the particle positions. The ingredients are:

`field`

. This is the density field. Should be a 3D float numpy array`BoxSize`

. Size of the density field. Units in Mpc/h`pos`

. These are the positions of the particles. Units in Mpc/h`density_interpolated`

. This is a 1D array with the value of the density field at the particle positions. Should be a numpy float array.

An example is this:

```
import MAS_library as MASL
# define the array containing the value of the density field at positions pos
density_interpolated = np.zeros(pos.shape[0], dtype=np.float32)
# find the value of the density field at the positions pos
MASL.CIC_interp(field, BoxSize, pos, density_interpolated)
```