Construct an array by executing a function over each coordinate.
The resulting array therefore has a value fn(x, y, z) at coordinate (x, y, z).
Parameters :  function : callable
shape : (N,) tuple of ints
dtype : datatype, optional


Returns :  out : any

Notes
Keywords other than shape and dtype are passed to function.
Examples
>>> np.fromfunction(lambda i, j: i == j, (3, 3), dtype=int)
array([[ True, False, False],
[False, True, False],
[False, False, True]], dtype=bool)
>>> np.fromfunction(lambda i, j: i + j, (3, 3), dtype=int)
array([[0, 1, 2],
[1, 2, 3],
[2, 3, 4]])