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Evaluation fail

asked 2015-03-29 05:35:31 -0500

deadalps gravatar image

updated 2015-03-30 16:14:43 -0500

tmonteil gravatar image

hello,

when running "0^0" the result is "1", but when defining "f(x)=0^x" and evaluating "f(0)" the evaluation fails with "ValueError: power::eval(): pow(0,0) is undefined". I guess this one is easy to fix... :)

version: Sage Version 6.5, Release Date: 2015-02-17

regards, manfred

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Using a python lambda function, this will work. That is, f = lambda x: 0^x will give a function that does what you want. So, this indicates that it is a matter of how Sage is defining its functions.

calc314 gravatar imagecalc314 ( 2015-03-29 08:15:25 -0500 )edit

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answered 2015-03-29 09:14:09 -0500

tmonteil gravatar image

updated 2015-03-30 16:15:22 -0500

When you write:

sage: f(x)=0^x

You define a "symbolic function":

sage: type(f)
<type 'sage.symbolic.expression.Expression'>
sage: f.parent()
Callable function ring with argument x

This is a kind of mathematical formula (like exp(cos(pi)) + log(x)). This is an object you can derivate, integrate, and so on.

Instead you can define a Python function:

sage: def f(x):
....:     return 0^x
sage: f(0)
1
sage: type(f)
<type 'function'>

For such easy-to-define function, you can be shorter, by typing:

sage: f = lambda x : 0^x
sage: f(0)
1
sage: type(f)
<type 'function'>

EDIT

According to your comment, it seems i misunderstood your question. Actually, the problem is not about evaluating the symbolic function f but about SR(0)^SR(0) being not defined. Thanks for reporting, @kcrisman opened trac ticket 18088.

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This is resolved in recent versions.

rws gravatar imagerws ( 2015-07-06 10:50:31 -0500 )edit
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answered 2015-03-30 09:08:44 -0500

deadalps gravatar image

updated 2015-03-30 09:49:23 -0500

well thanks for the fast answer but i already knew this "workarround" ;)

i reported this problem as i thought that this was a (very small) bug since pow(0,0) evaluates to 1. hence, it does not make any sense at all that the exception "pow(0,0) is undefined" is thrown.

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Asked: 2015-03-29 05:35:31 -0500

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Last updated: Mar 30 '15