This function is to calculate how likely the cells relevant to a gene set is randomly distributed spatially
# S3 method for spatial.kld
compute(spatial.coords, weight_vec, n = 10, n.times = 20)spatial kl-divergence
a data frame with each row as a cell and each column as a spatial coordinate (usually 2: x and y)
output of run.rwr
split the spatial map for local density estimation; n is the number of split for each dimension; for n = 10, the spatial map is split to n * n = 100 grids for the density estimation
the weight_vec is shuffled several times (n.times) to generate a background distribution (shuffled weights vs. equal weights) for statistical significance estimation (p.value); larger n.times will be more time-consuming and more accurate