Your function will be called *once*, with arguments that are *arrays* of coordinate values.  It must handle these arrays when it computes the values of the array to be created.

To see what is happening, print the values of i and j from within your function, e.g.:


In [57]: def ijsum(i, j):
   ....:     print "i =", i
   ....:     print "j =", j
   ....:     return i + j
   ....:

In [58]: fromfunction(ijsum, (3, 4))
i = [[ 0.  0.  0.  0.]
 [ 1.  1.  1.  1.]
 [ 2.  2.  2.  2.]]
j = [[ 0.  1.  2.  3.]
 [ 0.  1.  2.  3.]
 [ 0.  1.  2.  3.]]
Out[58]:
array([[ 0.,  1.,  2.,  3.],
       [ 1.,  2.,  3.,  4.],
       [ 2.,  3.,  4.,  5.]])


Your `myOnes` function will work if you modify it something like this:


In [59]: def myOnes(i, j):
   ....:     return np.ones(i.shape)
   ....:

In [60]: fromfunction(myOnes, (3, 4))
Out[60]:
array([[ 1.,  1.,  1.,  1.],
       [ 1.,  1.,  1.,  1.],
       [ 1.,  1.,  1.,  1.]])



The bug is in the docstring for fromfunction.  In the description of the `function` argument, it says "`function` must be capable of operating on arrays, and should return a scalar value."  But the function should *not* return a scalar value.  It should return an array of values appropriate for the given arguments.

Warren