Re: [sage-support] Re: bug in numerical evaluation of symbolic expression

[Vincent Delecroix]

On 25/04/16 17:49, William Stein wrote:

On Mon, Apr 25, 2016 at 12:06 PM, Volker Braun  wrote:

Presumable its because the RR nan doesn't correctly convert to the SR nan:

sage: NaN.is_zero()
False
sage: SR(RR('nan')).is_zero()
True


Related and confusing/wrong/inconsistent:

sage: RR('nan').is_zero()
True
sage: RR('nan') == 0
False


This is indeed wrong. The fix is at

http://trac.sagemath.org/ticket/20502

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Re: [sage-support] Re: bug in numerical evaluation of symbolic expression

[William Stein]

On Mon, Apr 25, 2016 at 12:06 PM, Volker Braun  wrote:
> Presumable its because the RR nan doesn't correctly convert to the SR nan:
>
> sage: NaN.is_zero()
> False
> sage: SR(RR('nan')).is_zero()
> True

Related and confusing/wrong/inconsistent:

sage: RR('nan').is_zero()
True
sage: RR('nan') == 0
False


>
>
>
> On Monday, April 25, 2016 at 7:40:39 PM UTC+2, William wrote:
>>
>> For a problem set I'm making today, I made up a random symbolic function,
>> then evaluated it and got confusing/inconsistent behavior.  See below:
>>
>> ~$ sage-develop
>> ┌┐
>> │ SageMath version 7.2.beta5, Release Date: 2016-04-21   │
>> │ Type "notebook()" for the browser-based notebook interface.│
>> │ Type "help()" for help.│
>> └┘
>> ┏┓
>> ┃ Warning: this is a prerelease version, and it may be unstable. ┃
>> ┗┛
>> sage: f(x) = e^(pi*x) + asin(x) + 1/(x^2 - x- e)
>> sage: f(1.1)   # should this be NaN since asin(x) not defined? What is
>> this output!? Print bug?
>> 1/(-e + 0.110) + e^(1.10*pi)
>> sage: N(f(1.1))  # yep
>> NaN
>> sage: N(1/(-e + 0.110) + e^(1.10*pi))   # What?
>> 31.2987079491022
>> sage: f(1.1).simplify()   # The NaN at the beginning makes sense...
>> NaN + 1/(-e + 0.1101) + e^(1.1*pi)
>>
>> I'm worried maybe there is a printing bug or something in f(1.1)...
>>
>> --
>> William (http://wstein.org)
>
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-- 
William (http://wstein.org)

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[sage-support] Re: bug in numerical evaluation of symbolic expression

[Volker Braun]

Presumable its because the RR nan doesn't correctly convert to the SR nan:

sage: NaN.is_zero()
False
sage: SR(RR('nan')).is_zero()
True



On Monday, April 25, 2016 at 7:40:39 PM UTC+2, William wrote:
>
> For a problem set I'm making today, I made up a random symbolic function, 
> then evaluated it and got confusing/inconsistent behavior.  See below: 
>
> ~$ sage-develop 
> ┌┐ 
> │ SageMath version 7.2.beta5, Release Date: 2016-04-21   │ 
> │ Type "notebook()" for the browser-based notebook interface.│ 
> │ Type "help()" for help.│ 
> └┘ 
> ┏┓ 
> ┃ Warning: this is a prerelease version, and it may be unstable. ┃ 
> ┗┛ 
> sage: f(x) = e^(pi*x) + asin(x) + 1/(x^2 - x- e) 
> sage: f(1.1)   # should this be NaN since asin(x) not defined? What is 
> this output!? Print bug? 
> 1/(-e + 0.110) + e^(1.10*pi) 
> sage: N(f(1.1))  # yep 
> NaN 
> sage: N(1/(-e + 0.110) + e^(1.10*pi))   # What? 
> 31.2987079491022 
> sage: f(1.1).simplify()   # The NaN at the beginning makes sense... 
> NaN + 1/(-e + 0.1101) + e^(1.1*pi) 
>
> I'm worried maybe there is a printing bug or something in f(1.1)... 
>
> -- 
> William (http://wstein.org) 
>

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