input: Write a function to calculate the running total of numbers in a given list using numpy. The function should return an array where each element at index `i` represents the sum of all elements from the start of the list up to index `i`. If the input list is empty, the function should return an empty list.
  
  import numpy as np
  
  def runningTotal(arr):
      return np.cumsum(arr)
  
  assert np.array_equal(runningTotal([1, 2, 3, 4]), [1, 3, 6, 10])
  assert np.array_equal(runningTotal([10, 20, 30]), [10, 30, 60])
  assert np.array_equal(runningTotal([]), [])
  assert np.array_equal(runningTotal([5]), [5])
  assert np.array_equal(runningTotal([-1, -2, -3]), [-1, -3, -6])
output: import numpy as np
  
  def runningTotal(arr):
      return np.cumsum(arr)