#17285: CIF is missing many functions
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Reporter: jdemeyer | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-6.4
Component: basic arithmetic | Resolution:
Keywords: | Merged in:
Authors: Vincent Delecroix | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/vdelecroix/17285 | dd4cf4e61cbc44485985e1f74de201c87ad06bc9
Dependencies: #17130 | Stopgaps:
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Comment (by vdelecroix):
Replying to [comment:9 jdemeyer]:
> I don't like the added complexity of having 3 branches in every
function. Why not just use the generic case everywhere?
The main reason is to avoid numerical noise (I want the cosine of a real
number to be a real number). You have
{{{
sage: a = CIF(2,0)
sage: I = CIF.gen()
sage: ((I*a).exp() + (-I*a).exp()) / 2
-0.4161468365471424? + 0.?e-16*I
}}}
It should be fine to remove the imaginary branch, but then it would be
less precise
{{{
sage: a = CIF(0,2)
sage: b1 = CIF(0, a.imag().cosh())
sage: b1.diameter()
1.33393183261575e-16
sage: b2 = ((I*a).exp() + (-I*a).exp()) / 2
sage: b2.diameter()
2.36079803558624e-16
}}}
Vincent
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Ticket URL: <http://trac.sagemath.org/ticket/17285#comment:10>
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