#8983: erf(0) should return 0
---------------------------+------------------------------------------------
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: |
---------------------------+------------------------------------------------
Old description:
> Currently it doesnt...
>
> {{{
> sage: solve(erf(x)==0,x)
> [erf(x) == 0]
> }}}
New description:
Currently it doesnt...
{{{
sage: erf(0)
erf(0)
}}}
--
Comment(by kcrisman):
You should always feel free to add patches - it's MUCH easier to tell what
people are talking about, even if the patch is really, really preliminary.
> (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?
This must be from an improvement in Maxima during the several recent
upgrades. I've updated the description.
> (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.
No, the usual practice is to not evaluate (give symbolic back) for "exact"
rings and evaluate (give numeric back) for "inexact" rings. There is some
disagreement among developers about exactly what these words mean, but
basically `erf(x),erf(1/2),erf(2),erf(e)` should all return something
symbolic and `erf(.1),erf(RDF(1))`, etc. should return something numeric.
I.e. `erf2)!=erf(2.)`.
>
> (4) Since I'm doing a bit more, should I open an enhancement ticket
instead?
I believe there already is a ticket for the complex pieces at #1173,
similarly at #9044. If you have a good solution to the whole thing, you
could do it at one of those and then say this ticket can be closed when
they are (if you have also documented that it's fixed.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8983#comment:6>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/sage-trac?hl=en.
