#16025: numerical inconsistency with exponential integral values Ei(x)
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Reporter: rws | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.2
Component: calculus | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by kcrisman):
Oh, dear. This is because we auto-evaluate things with decimal points.
{{{
sage: Ei(1.1)
2.16737827956340
sage: Ei(1.1).n(300)
2.16737827956340289858871983597055077552795410156250000000000000000000000000000000000000000
}}}
Not sure where those other things come from - floating point remains, I
guess? Especially since the last few digits are a power of two...
The `prec` deprecation was intended for things like
{{{
sage: Ei(1)
Ei(1)
sage: Ei(1).n(300)
1.89511781635593675546652093433163426901706058173270759164622843188251383453380415354890071
}}}
but apparently the warning happens no matter what. And if you read the
warning closely (!):
{{{
Explicitly set the precision of the input, for example
Ei(RealField(300)(1)), or use the prec argument to .n() for exact inputs,
e.g., Ei(1).n(300), instead.
}}}
So ... are you asking for more clarification of this (which I would
understand) or are you saying it is wrong? `1.1` is not "exact" so the
warning is telling us to explicitly set the precision of the input. Maybe
the example should be one that isn't exact, and say more about that being
appropriate then?
--
Ticket URL: <http://trac.sagemath.org/ticket/16025#comment:1>
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