PoissonRecon: Can't understand the function : NonLinearUpdateWeightContribution

I saw some poly functions in “NonLinearUpdateWeightContribution”

int i, j, k;
TreeOctNode::Neighbors& neighbors = neighborKey.setNeighbors(node);
double x, dxdy, dx[DIMENSION][3];
double width;
Point3D<Real> center;
Real w;
node->centerAndWidth(center, w);
width = w;
for (i = 0; i < DIMENSION; i++)
	{
		x = (center.coords[i] - position.coords[i] - width) / width;
		dx[i][0] = 1.125 + 1.500 * x + 0.500 * x * x;
		x = (center.coords[i] - position.coords[i]) / width;
		dx[i][1] = 0.750 - x * x;
		dx[i][2] = 1.0 - dx[i][1] - dx[i][0];
	}

and I don`t know what does x ,dxdy anddx mean , can you explain thanks