&& particle.x < grid.getXDimension() - 1
&& particle.y < grid.getYDimension() - 1) :
"particle.x=" + particle.x + "particle.y=" + particle.y ;
// adjust # particles as they cross cell boundaries
newHomeCell.incParticles(); // increment new cell
grid.getCell(i, j).decParticles(); // decrement last cell
particle.setCell( newHomeCell );
assert ( grid.getCell(i, j).getNumParticles() >= 0):
"The number of particles in grid[" + i + "][" + j + "] is " + grid.getCell(i, j).getNumParticles();