Electric current smoothing

For the finite difference models (em1d, em2d), the input parameters may also optionally define some smoothing (filtering) parameters to be applied to the electric current following the deposition of this quantity from particle motion. This is achieved through a call to the sim_set_smooth() routine:

void sim_set_smooth( t_simulation* sim, t_smooth* smooth)

This routine should be called inside sim_init(), somewhere after the call to sim_new(). Smoothing parameters are defined in the using a t_smooth structure:

Smoothing parameters	Description
xtype	Smoothing type along x. Must be one of NONE, BINOMIAL or COMPENSATED
xlevel	Number of passes of the smoothing kernel along x
ytype	(2D only) Same as xtype for the y direction
ylevel	(2D only) Same as xlevel for the y direction

For BINOMIAL smoothing, filtering is performed through a convolution of the grid data with a [1,2,1] kernel. This operation is repeated n times, where n is defined by the xlevel | ylevel parameters.

For COMPENSATED smoothing, the code will first apply BINOMIAL smoothing as described above, and will perform an additional pass with a specially calculated kernel that ensures that the filter transfer function near $k=0$ will be on the order of $1 + O(k^3)$, zeroing out $k^2$ dependencies. In pratice this leads to a filter that is flatter near $k=0$ and has a sharper drop near the cutoff frequency.

The following example sets up a 4th order COMPENSATED smoothing along the x direction:

void sim_init( t_simulation* sim ){

  (...)

  // Initialize Simulation data
  sim_new( sim, nx, box, dt, tmax, ndump, species, n_species );

  (...)

  // Set current smoothing (this must come after sim_new)
  t_smooth smooth = {
    .xtype = COMPENSATED,
    .xlevel = 4
  };

  sim_set_smooth( sim, &smooth );

  (...)
}