def drhody(field, data): return operators.d(data, 'Density', 1)
def dvydy(field, data): return operators.d(data, 'y-velocity', 1)
def dvzdz(field, data): return operators.d(data, 'z-velocity', 2)
def dvxdx(field, data): return operators.d(data, 'x-velocity', 0)