# Sympy integration algorithm towards -infinity

Following achrzesz hint about integral's algorithm option, I tried (Sage 4.7.2):

integral(1/x^2, x, -infinity, -1, algorithm='sympy')


Unfortunately, I got:

Traceback (click to the left of this block for traceback)
...
AttributeError: 'MinusInfinity' object has no attribute '_sympy_'


What's going wrong?

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1

The workarounds are good for now. I've opened the auspicious ticket # 12345 (http://trac.sagemath.org/sage_trac/ticket/12345) for the underlying issue.

( 2012-01-23 13:15:50 +0200 )edit

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It seems to be a bug. sympy can recognize infinity but not minus infinity of sage. You can try to directly call sympy integrate instead

import sympy as sp
a=sp.Symbol('a')
b=sp.integrate(1/x^2,(x,a,-1))._sage_()
b.substitute(a=-oo)

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How do you get this infinity symbol? But most importantly, do you input this code in a simple python interpreter or in Sage? What is this _sage_() method?

( 2012-01-23 11:50:43 +0200 )edit

How do you get this infinity symbol?

( 2012-01-23 11:50:44 +0200 )edit

Every element from another program (such as sympy) has a _sage_ method to convert its things back to Sage objects. The infinity symbol is just one of the several ways to represent infinity in Sage (and several other programs of this type); in principle, it should be equivalent to using infinity, but apparently this bug leaves it to not work for Sympy.

( 2012-01-23 13:17:32 +0200 )edit

All right, but how do you input the infinity symbol?

( 2012-01-23 13:21:14 +0200 )edit
1

-oo is just minus oo the alphabets

( 2012-01-23 13:59:56 +0200 )edit

sage: from sympy import *

sage: integrate(1/x^2, (x, -oo, -1), algorithm='sympy')

1

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How do you get this infinity symbol?? Anyway, I still get the same error even at the console using -infinity

( 2012-01-23 11:49:52 +0200 )edit

This works as of Sage 5.1 (see trac #12345). (Please tell me if old questions shouldn't be necromanced; I just add answers for future reference to questions where the issue has been fixed.)

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1

Seems fine to me! Or you could have commented under where I mentioned the ticket first, either is fine. Having complete info is good. Maybe we should close questions like that...

( 2013-06-05 21:52:07 +0200 )edit
1

I am not sure we should close such questions, or at least we should'nt delete them, since trac points to them, and we should keep examples, even if they are fixed. That said, it could be nice to have a better integration between ask and trac, as well as a system of 'categories' that allow to separate questions related to a sage bug or questions related to a failed build, or questions related to how to use sage (probably the most interesting for the readers). I am currently trying to do this via tags (removing bug tag where this is not a bug, and adding confirmed_bug or fixed_bug tag when this is a bug), but it is quite a long task, and having an automated link between ask and trac could be of great help.

( 2013-06-06 06:10:07 +0200 )edit

No, we shouldn't *delete* them; closing just means it's been resolved, I would say. But it's not really that important.

( 2013-06-06 13:17:24 +0200 )edit