import numpy as np

def symmetric_array(arr):
    sym_arr = np.zeros_like(arr)
    iu = np.triu_indices(arr.shape[0])
    sym_arr[iu] = arr[iu]
    il = np.tril_indices(arr.shape[0], k=-1)
    sym_arr[il] = arr.T[il]
    return sym_arr

arr = np.array([[1, 2, 3], [2, 4, 5], [3, 5, 6]])
sym_arr = symmetric_array(arr)
print(sym_arr)