#2562: [with patch, needs review] minor symbolic doc things
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Reporter: zimmerma | Owner: was
Type: enhancement | Status: new
Priority: minor | Milestone: sage-4.1.2
Component: calculus | Keywords:
Reviewer: Burcin Erocal | Author: Karl-Dieter Crisman
Merged: |
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Changes (by newvalueoldvalue):
* reviewer: => Burcin Erocal
* author: => Karl-Dieter Crisman
Comment:
I am confused with this exactness issue. Please excuse my ignorance of
floating point representation issues.
I don't understand what it means for an element of `RR` to be an ''exact
rational''. As far as I understand, the `.exact_rational()` function
returns the value stored in floating point representation as a rational
number (i.e., `mantissa*2^exp` ).
{{{
sage: RR(1/3).exact_rational()
6004799503160661/18014398509481984
sage: (1.9393).exact_rational()
8733830757359603/4503599627370496
}}}
However, these rationals don't represent the given value exactly.
{{{
sage: 1/3 - RR(1/3).exact_rational()
1/54043195528445952
sage: 19393/10000 - RR(1.9393).exact_rational()
-67/2814749767106560000
}}}
As opposed to:
{{{
sage: 37/16 - RR(37/16).exact_rational()
0
}}}
So in this case, can `1.9393` be called inexact?
I'd appreciate any reference where these issues are explained as well.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/2562#comment:5>
Sage <http://sagemath.org/>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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