input: Write a function to optimize a given multivariate function using the `scipy.optimize.minimize` method. The function should take a multivariate function and an initial guess as inputs and return the optimized values of the variables.
  assert optimize_function(lambda x: (x[0] - 1)**2 + (x[1] - 2.5)**2, [1, 0]) == [1.0, 2.5]
output: def optimize_function(func, initial_guess):
      from scipy.optimize import minimize
      result = minimize(func, initial_guess)
      return result.x