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Re: unary mapper system redesigned + a few questions
From: |
John W. Eaton |
Subject: |
Re: unary mapper system redesigned + a few questions |
Date: |
Tue, 17 Nov 2009 15:40:54 -0500 |
On 17-Nov-2009, Jaroslav Hajek wrote:
| No. Quoting the C++ standard:
|
| template<class T> complex<T> log(const complex<T>& x);
| Notes: the branch cuts are along the negative real axis.
|
| Returns: the complex natural (base e) logarithm of x, in the range of a
| strip mathematically unbounded
| along the real axis and in the interval [-i times pi, i times pi ]
| along the imaginary axis. When x is a
| negative real number, imag(log(x)) is pi.
|
| ..end of story.
Sorry, but I don't see why
(0, -1) / (large representable number)
should be considered to have a complex imaginary part yet
(0, -1) / inf
should not.
| > If you throw away the negative zero imaginary part before it even gets
| > to the log function, then there is no way to fix this problem.
| >
|
| Surely there is; just do
|
| y = complex (0, -1 ./ x)
|
| instead. "complex" skips the narrowing.
I don't see any practical way to do this for every computation which
might result in an underflow on the negative side of zero.
jwe
- Re: unary mapper system redesigned + a few questions, (continued)
- Re: unary mapper system redesigned + a few questions, John W. Eaton, 2009/11/12
- Re: unary mapper system redesigned + a few questions, Jaroslav Hajek, 2009/11/13
- Re: unary mapper system redesigned + a few questions, Jaroslav Hajek, 2009/11/13
- Re: unary mapper system redesigned + a few questions, Jaroslav Hajek, 2009/11/17
- Re: unary mapper system redesigned + a few questions, John W. Eaton, 2009/11/17
- Re: unary mapper system redesigned + a few questions, Jaroslav Hajek, 2009/11/17
- Re: unary mapper system redesigned + a few questions, John W. Eaton, 2009/11/17
- Re: unary mapper system redesigned + a few questions, Jaroslav Hajek, 2009/11/17
- Re: unary mapper system redesigned + a few questions, John W. Eaton, 2009/11/17
- Re: unary mapper system redesigned + a few questions, Jaroslav Hajek, 2009/11/17
- Re: unary mapper system redesigned + a few questions,
John W. Eaton <=
- Re: unary mapper system redesigned + a few questions, Jaroslav Hajek, 2009/11/18
- Re: unary mapper system redesigned + a few questions, Judd Storrs, 2009/11/18
- Re: unary mapper system redesigned + a few questions, John W. Eaton, 2009/11/18
- Re: unary mapper system redesigned + a few questions, Jaroslav Hajek, 2009/11/18
- Re: unary mapper system redesigned + a few questions, Judd Storrs, 2009/11/18
- Re: unary mapper system redesigned + a few questions, Jaroslav Hajek, 2009/11/18
- Re: unary mapper system redesigned + a few questions, John W. Eaton, 2009/11/18
- Re: unary mapper system redesigned + a few questions, Jaroslav Hajek, 2009/11/18
- Re: unary mapper system redesigned + a few questions, Jaroslav Hajek, 2009/11/18
- Re: unary mapper system redesigned + a few questions, John W. Eaton, 2009/11/18