On Thu, Jul 19, 2012 at 5:52 AM, Cheng Li <scrappedprince...@gmail.com>wrote:
> Hi All,****
>
> ** **
>
> I have spot a strange behavior of numpy.fromfunction(). The sample codes
> are as follows:****
>
> >>> import numpy as np****
>
> >>> def myOnes(i,j):****
>
> return 1.0****
>
> >>> a = np.fromfunction(myOnes,(2000,2000))****
>
> >>> a****
>
> 1.0****
>
> ** **
>
> Actually what I expected is that the function will return a 2000*2000 2d
> array with unit value. The returned single float value really confused me.
> Is this a known bug? The numpy version I used is 1.6.1.****
>
> **
>
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
> **
>
> Regards,****
>
> Cheng****
>
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