#13193: erf evaluation is wrong along imaginary axis
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Reporter: kcrisman | Owner: jason, jkantor
Type: defect | Status: new
Priority: critical | Milestone: sage-5.2
Component: numerical | Keywords:
Work issues: | Report Upstream: N/A
Reviewers: | Authors:
Merged in: | Dependencies:
Stopgaps: |
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This was first noted at [http://ask.sagemath.org/question/1571/plot-
solution-for-y-2xy-1 this ask.sagemath.org question]. Here are ''some''
of the symptoms.
* Being off by a real part of 1 along the imaginary axis
{{{
sage: for z in [3,33,333,3333]:
....: mpmath.erf(i*z); erf(n(z)*i)
....:
mpc(real='0.0', imag='1629.9946226015657')
1.00000000000000 + 1629.86732385786*I
mpc(real='0.0', imag='1.5128697751040891e+471')
1.00000000000000 + 1.51286977510409e471*I
mpc(real='0.0', imag='5.1260939089106243e+48155')
1.00000000000000 + 5.12609390891062e48155*I
mpc(real='0.0', imag='2.6385510598470926e+4824525')
1.00000000000000 + 2.63855105984709e4824525*I
}}}
* Starting to be wrong in the imaginary component as well as the number
gets closer to 0
{{{
sage: pari(3*i).erfc()
-1.76710569338983 E-16 - 1629.86732385786*I
sage: mpmath.erfc(3*i)
mpc(real='1.0', imag='-1629.9946226015657')
sage: 1-pari(3*i).erfc()
1.00000000000000 + 1629.86732385786*I
sage: mpmath.erf(3*i)
mpc(real='0.0', imag='1629.9946226015657')
sage: erf(i*1.42)
1.00000000000000 + 4.03986343036907*I
sage: import mpmath
sage: mpmath.erf(i*1.42)
mpc(real='0.0', imag='3.8217653554366318')
}}}
Ideally this would be fixed by #1173 or #13050, but if there is something
else we can do (and soon) that would be fine too.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13193>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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