#9953: int(symbolic expr) off by 1
-------------------------+--------------------------------------------------
Reporter: schilly | Owner: burcin
Type: defect | Status: new
Priority: critical | Milestone: sage-4.6
Component: symbolics | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Problem, last digit is either 6 or 7. In short:
{{{
fermat(n) = 2**2**n + 1
fermat(9) gives ....4097 but:
int(fermat(9)) gives ...4096L.
Same with: long(fermat(9)).
int(2**2**9 +1) gives ...4097L
}}}
Burcin says: int(x) for a symbolic expression x just calls
int(x.n(prec=100)). We lose that 1 in the approximation.
full example in 4.5.2:
{{{
sage: fermat(n) = 2**2**n + 1
sage: fermat(9)
134078079299425970995740249982058461274793658205923933777\
235614437217640300735469768018742981669034276900318581864\
86050853753882811946569946433649006084097
sage: int(fermat(9))
134078079299425970995740249982058461274793658205923933777\
235614437217640300735469768018742981669034276900318581864\
86050853753882811946569946433649006084096L
sage: long(fermat(9))
134078079299425970995740249982058461274793658205923933777\
235614437217640300735469768018742981669034276900318581864\
86050853753882811946569946433649006084096L
sage: int(2**2**9 +1)
134078079299425970995740249982058461274793658205923933777\
235614437217640300735469768018742981669034276900318581864\
86050853753882811946569946433649006084097L
}}}
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/9953>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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