Modify the sampling to use a CDF.

[bluescarni]

This should guarantee that exactly the number of samples requested is generated, if no minimum number of samples per cell is specified.

[bluescarni]

@astrofrog I ran some tests to verify that the output makes sense. For instance, let's take a grid with 1000 sites and 1E6 sampling points requested (with no minimum number of samples per cell):

>>> from hyperion.grid import voronoi_helpers as vh
>>> import numpy as np
>>> N = 1000
>>> x,y,z = [np.random.uniform(size=N) for _ in range(3)]
>>> sites_arr = np.array([x, y, z]).transpose()
>>> g = vh.voronoi_grid(sites_arr, np.array([[0, 1.], [0, 1], [0, 1]]),n_samples=1000000,min_cell_samples=0)

Now:

>>> len(g.samples)
1000000

In order to verify the consistency:

>>> np.diff(g.samples_idx) / g.neighbours_table['volume']
<Column name='volume' unit=None format=None description=None>
array([ 1018694.15040659,  1080715.16884351,   976212.09429447,
        1098848.13745834,  1008257.2629003 ,  1032139.54447319,
        1018753.84790525,  1005302.99701911,  1078185.42701527,
         991726.70469929,   976558.35358736,   978557.28966799,
        1072755.41271036,   904619.75511727,  1043178.37164639,
         985434.55154042,  1074977.81301676,   978790.20543328,
         972130.46901091,  1068138.72618046,  1035370.55618304,
         999640.36688186,  1037506.31109164,   970565.7576943 ,
        1010189.57693786,   996529.92285498,  1021826.53152044,
         984787.45982084,  1021248.37949541,   989204.98248675,

That is, the ratio between cell volume and number of samples in that cell is more or less constant.

Does this make sense to you?

[astrofrog]

@bluescarni - looks great, thanks!