[sage-support] Re: [sage-cell] Where Oh Where is my Divide By Zero Error?

2018-03-20 Thread John H Palmieri 


On Friday, March 16, 2018 at 7:29:30 PM UTC-7, A. Jorge Garcia wrote:
>
> Thanks! 
>
> On Fri, Mar 16, 2018, 10:27 PM Andrey Novoseltsev  > wrote:
>
>> On Fri, Mar 16, 2018 at 4:18 PM, Jorge Garcia > > wrote:
>> > Dear Hive Mind:
>> >
>> > Why is there no Divide By Zero Error here:
>> > 
>> http://sagecell.sagemath.org/?z=eJwljkELgkAUhO-C_2GiAtek1kuX2Eu4pBc3NjEqCqQ2E-QlpvX3cwuGd5jHzDdjZHGyw6BUZdgoFQXYx1JLa2WxRJTkSSSxPuAotYLUWumR64zRcDEJOecBtFhOA3QitHZpyLRFZ1BR03fDvdb9raISJLjrpKItqDReyNnq9Xh-vJTZkHkXdW9DjUcMvu__F2SIlNxhk-Tyt-UHH76usxUny_a9cMbnfLkgdiHcny1oICI9_8u37AuZcDtw=sage
>> >
>> > But there is a Divide By Zero Error here (as expected):
>> > 
>> http://sagecell.sagemath.org/?z=eJwlj0FLw0AQhe-B_IcnVcimQTeXXmQPtRnsXrJhG6q2WAh2GwtlGmKif9_dBoY5zJvvzZsZ6rXewNerMUWGNwK9V7SqsUSht7ogvHxgR9aArDX2Lo5m6KS6z6WUGaxaPGQYVB5HXcJChWma5HP5KBdPLA78_PN9_UuCJgLZOnZ9MzicuRsH378u4_HMLVjJOCpV33DrklyKiStvkPttLmOAgg3SNF2TJegahSGfW2_JP0FTPq_GUaX2t9XTtQf7Iyg_J79K_AMYbUA7=sage
>> >
>> > Can someone please explain this to me? This came up in class and I was
>> > looking for a "teachable moment" asking the students to fix the Divide 
>> By
>> > Zero Error like this:
>> > 
>> http://sagecell.sagemath.org/?z=eJwljkFrg0AUhO-C_2GKKbhW0t1LLmUvwddmLxq2EtKWBKTZWkGeYjX5-3XjbXgz37yJkJmDyQjbD3ySLUDWFhav5kjZQxhE6KVeKSllCqs3jylGrcKgj1lof01i9STXcvPM4swvf7_dLfae8GTt2A3V6NBwP43Ii3JW3-10abgGaxkGuR4qrl2sUiXFQud31F2rdvKoL0OSJDuyBFMiK-gdb-ZAKHe0bJ3dMNjrr3v0pxvA8xvkp6VvL_4B6uc8qg===sage
>> >
>> > Thanx,
>> > AJG
>>
>> Someone probably can, but perhaps not on this list: it has something
>> to do with 0^0 evaluating to 1 and I recall some earlier discussions
>> about it. Forwarding to sage-support.
>>
>
Maybe related to this:

sage: 2/0
---
ZeroDivisionError Traceback (most recent call last)
 in ()
> 1 Integer(2)/Integer(0)

/Users/palmieri/Desktop/Sage_stuff/sage_builds/VANILLA/sage-8.2.beta8/local/lib/python2.7/site-packages/sage/rings/integer.pyx
 
in sage.rings.integer.Integer.__div__ 
(build/cythonized/sage/rings/integer.c:13231)()
   1910 if type(left) is type(right):
   1911 if mpz_sgn((right).value) == 0:
-> 1912 raise ZeroDivisionError("rational division by zero")
   1913 x =  Rational.__new__(Rational)
   1914 mpq_div_zz(x.value, (left).value, 
(right).value)

ZeroDivisionError: rational division by zero
sage: 2.0/0
+infinity

I don't like this behavior much. What is the rationale? In inexact rings, 
zero division is not a thing?

-- 
John

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Re: [sage-support] Re: [sage-cell] Where Oh Where is my Divide By Zero Error?

2018-03-20 Thread Ralf Stephan 
On Sunday, March 18, 2018 at 5:19:07 PM UTC+1, Johan S. H. Rosenkilde wrote:
>
> I don't have a better explanation for why this difference has been 
> adopted in Sage than the above: following IEEE standard vs doing the 
> mathematically safe-and-fail-early-solution. Perhaps someone more 
> knowledgeable about this can chime in. 
>

Historically throwing this specific error was introduced with the massive 
effort of adapting GiNaC to Sage (2008-2012). There are various errors you 
can get by triggering different code parts. Another in symbolics:

sage: SR(1)/0
...
ZeroDivisionError: Symbolic division by zero

Regards,

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Re: [sage-support] Re: [sage-cell] Where Oh Where is my Divide By Zero Error?

2018-03-18 Thread Johan S. H. Rosenkilde 
Hi,

It is not related to exponentiation; it is due to the difference between
symbolic evaluation and real-valued evaluation when dividing by zero.

Real-valued arithmetic mirrors the IEEE floating point standard, I expect:

sage: 1.0/0
+infinity

While symbolic evaluation gives the divide-by-zero error:

sage: expr = 1.0/x
sage: expr(x=0)

Traceback (most recent call last)
...
ValueError: power::eval(): division by zero

Note that the inline-function-notation "p(n) = ..." is really just
defining a symbolic expression. In the above snippet I rely on x being a
symbolic variable in a fresh Sage instance, thereby avoiding writing
"expr(x) = ...".

I don't have a better explanation for why this difference has been
adopted in Sage than the above: following IEEE standard vs doing the
mathematically safe-and-fail-early-solution. Perhaps someone more
knowledgeable about this can chime in.

Best,
Johan


Andrey Novoseltsev writes:

> On Fri, Mar 16, 2018 at 4:18 PM, Jorge Garcia  wrote:
>> Dear Hive Mind:
>>
>> Why is there no Divide By Zero Error here:
>> http://sagecell.sagemath.org/?z=eJwljkELgkAUhO-C_2GiAtek1kuX2Eu4pBc3NjEqCqQ2E-QlpvX3cwuGd5jHzDdjZHGyw6BUZdgoFQXYx1JLa2WxRJTkSSSxPuAotYLUWumR64zRcDEJOecBtFhOA3QitHZpyLRFZ1BR03fDvdb9raISJLjrpKItqDReyNnq9Xh-vJTZkHkXdW9DjUcMvu__F2SIlNxhk-Tyt-UHH76usxUny_a9cMbnfLkgdiHcny1oICI9_8u37AuZcDtw=sage
>>
>> But there is a Divide By Zero Error here (as expected):
>> http://sagecell.sagemath.org/?z=eJwlj0FLw0AQhe-B_IcnVcimQTeXXmQPtRnsXrJhG6q2WAh2GwtlGmKif9_dBoY5zJvvzZsZ6rXewNerMUWGNwK9V7SqsUSht7ogvHxgR9aArDX2Lo5m6KS6z6WUGaxaPGQYVB5HXcJChWma5HP5KBdPLA78_PN9_UuCJgLZOnZ9MzicuRsH378u4_HMLVjJOCpV33DrklyKiStvkPttLmOAgg3SNF2TJegahSGfW2_JP0FTPq_GUaX2t9XTtQf7Iyg_J79K_AMYbUA7=sage
>>
>> Can someone please explain this to me? This came up in class and I was
>> looking for a "teachable moment" asking the students to fix the Divide By
>> Zero Error like this:
>> http://sagecell.sagemath.org/?z=eJwljkFrg0AUhO-C_2GKKbhW0t1LLmUvwddmLxq2EtKWBKTZWkGeYjX5-3XjbXgz37yJkJmDyQjbD3ySLUDWFhav5kjZQxhE6KVeKSllCqs3jylGrcKgj1lof01i9STXcvPM4swvf7_dLfae8GTt2A3V6NBwP43Ii3JW3-10abgGaxkGuR4qrl2sUiXFQud31F2rdvKoL0OSJDuyBFMiK-gdb-ZAKHe0bJ3dMNjrr3v0pxvA8xvkp6VvL_4B6uc8qg===sage
>>
>> Thanx,
>> AJG
>
> Someone probably can, but perhaps not on this list: it has something
> to do with 0^0 evaluating to 1 and I recall some earlier discussions
> about it. Forwarding to sage-support.

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[sage-support] Re: [sage-cell] Where Oh Where is my Divide By Zero Error?

2018-03-16 Thread Jorge Garcia 
Thanks!

On Fri, Mar 16, 2018, 10:27 PM Andrey Novoseltsev 
wrote:

> On Fri, Mar 16, 2018 at 4:18 PM, Jorge Garcia  wrote:
> > Dear Hive Mind:
> >
> > Why is there no Divide By Zero Error here:
> >
> http://sagecell.sagemath.org/?z=eJwljkELgkAUhO-C_2GiAtek1kuX2Eu4pBc3NjEqCqQ2E-QlpvX3cwuGd5jHzDdjZHGyw6BUZdgoFQXYx1JLa2WxRJTkSSSxPuAotYLUWumR64zRcDEJOecBtFhOA3QitHZpyLRFZ1BR03fDvdb9raISJLjrpKItqDReyNnq9Xh-vJTZkHkXdW9DjUcMvu__F2SIlNxhk-Tyt-UHH76usxUny_a9cMbnfLkgdiHcny1oICI9_8u37AuZcDtw=sage
> >
> > But there is a Divide By Zero Error here (as expected):
> >
> http://sagecell.sagemath.org/?z=eJwlj0FLw0AQhe-B_IcnVcimQTeXXmQPtRnsXrJhG6q2WAh2GwtlGmKif9_dBoY5zJvvzZsZ6rXewNerMUWGNwK9V7SqsUSht7ogvHxgR9aArDX2Lo5m6KS6z6WUGaxaPGQYVB5HXcJChWma5HP5KBdPLA78_PN9_UuCJgLZOnZ9MzicuRsH378u4_HMLVjJOCpV33DrklyKiStvkPttLmOAgg3SNF2TJegahSGfW2_JP0FTPq_GUaX2t9XTtQf7Iyg_J79K_AMYbUA7=sage
> >
> > Can someone please explain this to me? This came up in class and I was
> > looking for a "teachable moment" asking the students to fix the Divide By
> > Zero Error like this:
> >
> http://sagecell.sagemath.org/?z=eJwljkFrg0AUhO-C_2GKKbhW0t1LLmUvwddmLxq2EtKWBKTZWkGeYjX5-3XjbXgz37yJkJmDyQjbD3ySLUDWFhav5kjZQxhE6KVeKSllCqs3jylGrcKgj1lof01i9STXcvPM4swvf7_dLfae8GTt2A3V6NBwP43Ii3JW3-10abgGaxkGuR4qrl2sUiXFQud31F2rdvKoL0OSJDuyBFMiK-gdb-ZAKHe0bJ3dMNjrr3v0pxvA8xvkp6VvL_4B6uc8qg===sage
> >
> > Thanx,
> > AJG
>
> Someone probably can, but perhaps not on this list: it has something
> to do with 0^0 evaluating to 1 and I recall some earlier discussions
> about it. Forwarding to sage-support.
>

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[sage-support] Re: [sage-cell] Where Oh Where is my Divide By Zero Error?

2018-03-16 Thread Andrey Novoseltsev 
On Fri, Mar 16, 2018 at 4:18 PM, Jorge Garcia  wrote:
> Dear Hive Mind:
>
> Why is there no Divide By Zero Error here:
> http://sagecell.sagemath.org/?z=eJwljkELgkAUhO-C_2GiAtek1kuX2Eu4pBc3NjEqCqQ2E-QlpvX3cwuGd5jHzDdjZHGyw6BUZdgoFQXYx1JLa2WxRJTkSSSxPuAotYLUWumR64zRcDEJOecBtFhOA3QitHZpyLRFZ1BR03fDvdb9raISJLjrpKItqDReyNnq9Xh-vJTZkHkXdW9DjUcMvu__F2SIlNxhk-Tyt-UHH76usxUny_a9cMbnfLkgdiHcny1oICI9_8u37AuZcDtw=sage
>
> But there is a Divide By Zero Error here (as expected):
> http://sagecell.sagemath.org/?z=eJwlj0FLw0AQhe-B_IcnVcimQTeXXmQPtRnsXrJhG6q2WAh2GwtlGmKif9_dBoY5zJvvzZsZ6rXewNerMUWGNwK9V7SqsUSht7ogvHxgR9aArDX2Lo5m6KS6z6WUGaxaPGQYVB5HXcJChWma5HP5KBdPLA78_PN9_UuCJgLZOnZ9MzicuRsH378u4_HMLVjJOCpV33DrklyKiStvkPttLmOAgg3SNF2TJegahSGfW2_JP0FTPq_GUaX2t9XTtQf7Iyg_J79K_AMYbUA7=sage
>
> Can someone please explain this to me? This came up in class and I was
> looking for a "teachable moment" asking the students to fix the Divide By
> Zero Error like this:
> http://sagecell.sagemath.org/?z=eJwljkFrg0AUhO-C_2GKKbhW0t1LLmUvwddmLxq2EtKWBKTZWkGeYjX5-3XjbXgz37yJkJmDyQjbD3ySLUDWFhav5kjZQxhE6KVeKSllCqs3jylGrcKgj1lof01i9STXcvPM4swvf7_dLfae8GTt2A3V6NBwP43Ii3JW3-10abgGaxkGuR4qrl2sUiXFQud31F2rdvKoL0OSJDuyBFMiK-gdb-ZAKHe0bJ3dMNjrr3v0pxvA8xvkp6VvL_4B6uc8qg===sage
>
> Thanx,
> AJG

Someone probably can, but perhaps not on this list: it has something
to do with 0^0 evaluating to 1 and I recall some earlier discussions
about it. Forwarding to sage-support.

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