Grids are not centered when dimension is not divisible by resolution

[mattragoza]

The centering of grids appears to depend on the dimension argument- the output grids are only centered at the provided center if dimension is divisible by resolution. See the following example:

import molgrid, torch

# single atom with radius=1.0 located at (0,0,0)
coords = torch.zeros((1, 3), device='cuda')
types = torch.ones((1, 1), device='cuda')
radii = torch.ones((1,), device='cuda')

# two grid makers with resolution=1.0 and center=(0,0,0)
#   with same size (# points) but different "dimensions"

gridder1 = molgrid.Coords2Grid(
    gmaker=molgrid.GridMaker(
        resolution=1.0,
        dimension=2.0,
    ),
    center=(0,0,0)
)
gridder2 = molgrid.Coords2Grid(
    gmaker=molgrid.GridMaker(
        resolution=1.0,
        dimension=1.9,
    ),
    center=(0,0,0)
)

grid1 = gridder1.forward(coords, types, radii)
grid2 = gridder2.forward(coords, types, radii)

print('grids have the same shape:', grid1.shape == grid2.shape)
print('grids have the same values:', (grid1 == grid2).all().item())

m = tuple(dim//2 for dim in grid1.shape) # midpoint index
print('grid1 is centered at (0,0,0):', (grid1[m] == 1.0).item())
print('grid2 is centered at (0,0,0):', (grid2[m] == 1.0).item())

def check_symmetry(grid):
    return (
        (grid == grid.flip(dims=(1,))).all() and
        (grid == grid.flip(dims=(2,))).all() and
        (grid == grid.flip(dims=(3,))).all()
    ).item()

print('grid1 is symmetric:', check_symmetry(grid1))
print('grid2 is symmetric:', check_symmetry(grid2))

Which produces this output:

grids have the same shape: True
grids have the same values: False
grid1 is centered at (0,0,0): True
grid2 is centered at (0,0,0): False
grid1 is symmetric: True
grid2 is symmetric: False