input: Write a python function to calculate the area of an ellipse given its semi-major and semi-minor axes.
  assert calculate_ellipse_area(5, 3) == 47.12388980384689
  assert calculate_ellipse_area(7, 4) == 87.96459430051421
  assert calculate_ellipse_area(10, 2) == 62.83185307179586
output: def calculate_ellipse_area(a, b):
      import math
      return math.pi * a * b