#5047: [with patch, positive review pending changes] comparing complex i raises
error
------------------------------+---------------------------------------------
Reporter: burcin | Owner: somebody
Type: defect | Status: new
Priority: major | Milestone: sage-3.3
Component: basic arithmetic | Resolution:
Keywords: |
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Comment (by SimonKing):
The second patch `cmp_doc.patch` (to be applied after the first patch)
adds more documentation.
Replying to [comment:3 burcin]:
> I ran into this when testing new printing code in pynac. ATM, pynac uses
the sign function, which is defined to be cmp(x, 0), to determine if it
should print a minus sign. Thus, we have the following:
>
> {{{
> sage: var('x',ns=1)
> sage: i*x
> <boom>
> }}}
Ok, but I think there should be a different approach for determining the
sign when printing an imaginary number.
However, personally I believe that `sign(I)` should raise an error.
> I somehow thought that the cmp function was not supposed to raise
exceptions, but googling shortly didn't turn up any evidence to support
this argument.
... and, as I mentioned above, `cmp` does raise an exception in Python.
> BTW, the sign function is also mentioned here: #777
The `sign` function defined in #777 would simply return 0 on non-real
constants, because it tests `bool(x > 0)`. Indeed, we have
{{{
sage: bool(I > 0)
False
sage: bool(I < 0)
False
}}}
so, at least it does not go boom (which it ''should'', though!).
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5047#comment:4>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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