Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
On Jan 4, 2008 12:27 PM, Andrew Straw [EMAIL PROTECTED] wrote: I have added a page to the wiki describing this issue: http://scipy.org/numpy_warts_and_gotchas I'll link it into the main documentation pages over the next few days, but I ask for a review the following text for correctness and clarity: (You can simply edit the wiki page or post your reply here and I'll do it.) Like most of numpy, allclose() uses the broadcasting rules when performing its operation. This leads to the following behavior: a=32 b=numpy.array([]) numpy.allclose(a,b) True Upon closer inspection, we can see that the broadcasting rules cause a to become a zero-dimensional array like b. The default truth value of a It is not the dimensions, it's the fact that the array is empty, so that anything said about it's non-existent elements is true, i.e., x in empty - anything is always true because x in empty is always false. So we also have the following: In [1]: allclose(32,[[]]) Out[1]: True The other reason is that because of broadcasting, the shape of the arrays may be immaterial. Chuck ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
I have added a page to the wiki describing this issue: http://scipy.org/numpy_warts_and_gotchas I'll link it into the main documentation pages over the next few days, but I ask for a review the following text for correctness and clarity: (You can simply edit the wiki page or post your reply here and I'll do it.) Like most of numpy, allclose() uses the broadcasting rules when performing its operation. This leads to the following behavior: a=32 b=numpy.array([]) numpy.allclose(a,b) True Upon closer inspection, we can see that the broadcasting rules cause a to become a zero-dimensional array like b. The default truth value of a zero-dimensional array is True, so the following holds and illustrates how the above result is consistent with numpy's rules. Andrew Straw wrote: Apologies if I've missed the discussion of this, but I was recently surprised by the following behavior (in svn trunk 4673). The following code runs without triggering the assertion. import numpy as np print np.__version__ a=np.int32(42) b=np.array([],dtype=np.int32) assert np.allclose(a,b) Is this expected behavior of numpy or is this a bug I should report? Thanks, Andrew ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
Thanks, I updated the page. Charles R Harris wrote: On Jan 4, 2008 12:27 PM, Andrew Straw [EMAIL PROTECTED] mailto:[EMAIL PROTECTED] wrote: I have added a page to the wiki describing this issue: http://scipy.org/numpy_warts_and_gotchas I'll link it into the main documentation pages over the next few days, but I ask for a review the following text for correctness and clarity: (You can simply edit the wiki page or post your reply here and I'll do it.) Like most of numpy, allclose() uses the broadcasting rules when performing its operation. This leads to the following behavior: a=32 b=numpy.array([]) numpy.allclose(a,b) True Upon closer inspection, we can see that the broadcasting rules cause a to become a zero-dimensional array like b. The default truth value of a It is not the dimensions, it's the fact that the array is empty, so that anything said about it's non-existent elements is true, i.e., x in empty - anything is always true because x in empty is always false. So we also have the following: In [1]: allclose(32,[[]]) Out[1]: True The other reason is that because of broadcasting, the shape of the arrays may be immaterial. Chuck ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
[Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
Apologies if I've missed the discussion of this, but I was recently surprised by the following behavior (in svn trunk 4673). The following code runs without triggering the assertion. import numpy as np print np.__version__ a=np.int32(42) b=np.array([],dtype=np.int32) assert np.allclose(a,b) Is this expected behavior of numpy or is this a bug I should report? Thanks, Andrew ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
Andrew Straw wrote: Apologies if I've missed the discussion of this, but I was recently surprised by the following behavior (in svn trunk 4673). The following code runs without triggering the assertion. import numpy as np print np.__version__ a=np.int32(42) b=np.array([],dtype=np.int32) assert np.allclose(a,b) Is this expected behavior of numpy or is this a bug I should report? Bug, I think. -- Robert Kern I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth. -- Umberto Eco ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
On Jan 3, 2008 1:06 PM, Robert Kern [EMAIL PROTECTED] wrote: Andrew Straw wrote: Apologies if I've missed the discussion of this, but I was recently surprised by the following behavior (in svn trunk 4673). The following code runs without triggering the assertion. import numpy as np print np.__version__ a=np.int32(42) b=np.array([],dtype=np.int32) assert np.allclose(a,b) Is this expected behavior of numpy or is this a bug I should report? Bug, I think. Isn't it trivially true that all elements of an empty array are close to any number? For instance, it is a well known fact that all blue, cheese eating martians speak esperanto. Chuck ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
On Thu, 3 Jan 2008, Charles R Harris apparently wrote: Isn't it trivially true that all elements of an empty array are close to any number? Sure, but might not one expect a ValueError due to shape mismatch? (Doesn't allclose usually use normal broadcasting rules?) Cheers, Alan Isaac ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
Hi, import numpy as np print np.__version__ a=np.int32(42) b=np.array([],dtype=np.int32) assert np.allclose(a,b) Is this expected behavior of numpy or is this a bug I should report? Bug, I think. I think this bug - which may be mine - follows from this line in allclose: return all(less_equal(absolute(x-y), atol + rtol * absolute(y))) and: In [39]: all([]) Out[39]: True Matthew ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
On Thu, 3 Jan 2008, Charles R Harris apparently wrote: Isn't it trivially true that all elements of an empty array are close to any number? On Thu, 3 Jan 2008, Alan G Isaac apparently wrote: Sure, but might not one expect a ValueError due to shape mismatch? (Doesn't allclose usually use normal broadcasting rules?) Ooops, forgot that was a scalar, so it was normal: a*b array([], dtype=int32) Cheers, Alan Isaac ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
Just to ask - is there a reason why this: In [39]: all([]) Out[39]: True is the case? ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
On Jan 3, 2008 2:37 PM, Matthew Brett [EMAIL PROTECTED] wrote: Just to ask - is there a reason why this: In [39]: all([]) Out[39]: True is the case? Because it's True. Anything is true about the elements of an empty set, because there aren't any. In this case, all asks if all elements in [] are true, i.e., does x member [] - x is true. Since x member [] is always false, the implication is always true. Recall that the statement x - y has the same truth value as the statement x' or xy. Chuck ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
So, currently we have all and allclose giving the same answer: In [19]: a = array([]) In [20]: b = array([1]) In [21]: all(a == b) Out[21]: True In [22]: allclose(a, b) Out[22]: True Would we want the answers to be different? ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
Matthew Brett wrote: So, currently we have all and allclose giving the same answer: In [19]: a = array([]) In [20]: b = array([1]) In [21]: all(a == b) Out[21]: True In [22]: allclose(a, b) Out[22]: True Would we want the answers to be different? No. I wasn't thinking correctly, previously. -- Robert Kern I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth. -- Umberto Eco ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
So, currently we have all and allclose giving the same answer: In [19]: a = array([]) In [20]: b = array([1]) In [21]: all(a == b) Out[21]: True In [22]: allclose(a, b) Out[22]: True Would we want the answers to be different? No. I wasn't thinking correctly, previously. It's unfortunate that all of us immediately think the given answer is wrong. ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] unexpected behavior with allclose( scalar, empty array)
Matthew Brett wrote: So, currently we have all and allclose giving the same answer: In [19]: a = array([]) In [20]: b = array([1]) In [21]: all(a == b) Out[21]: True In [22]: allclose(a, b) Out[22]: True Would we want the answers to be different? No. I wasn't thinking correctly, previously. It's unfortunate that all of us immediately think the given answer is wrong. Maybe we need allclose_sameshape() (my ability to name stuff is terrible, but you get the idea). Regardless of the name issue, I have no idea how this is viewed against the no-namespace-bloat principle. ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
