#8983: erf(0) should return 0
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Reporter: rossk | Owner: RossK
Type: enhancement | Status: new
Priority: minor | Milestone: sage-4.6.2
Component: symbolics | Keywords: erf, beginner
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Comment(by dsm):
Beginner reporting for duty! So I have a patch which sets erf(0) to 0 --
or, rather, to parent(x)(0) if x==0, so that it's the "right" zero; I
think this is the right idiom -- and adds complex arguments from mpmath.
But I have a few questions that came up along the way:
(1) In 4.6.1, solve(erf(x)==0,x) seems to work for me already, before the
patch. Did I get my binaries confused somehow, or did something change
elsewhere?
(2) It'd be nice if #8720 (fixing str(CC(0))) were finished, it surprised
me when writing tests for the zero type preservation. Maybe I should have
a look, I think it's mostly fixing some doctests left.
(3) My patch broke a doctest in functions/special.py, which expected
erf(0.5) to be evaluated to 0.520499877813047, but the existing doctests
for erf demand that erf(2) = erf(2). I can get that behaviour, namely to
evaluate for reals and to hold for integers except for zero, but I don't
quite follow it.
(4) Since I'm doing a bit more, should I open an enhancement ticket
instead?
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8983#comment:5>
Sage <http://www.sagemath.org>
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