[Numpy-discussion] Log Arrays

Charles R Harris charlesr.harris@gmail....
Thu May 8 13:53:08 CDT 2008


On Thu, May 8, 2008 at 12:39 PM, Anne Archibald <peridot.faceted@gmail.com>
wrote:

> 2008/5/8 Charles R Harris <charlesr.harris@gmail.com>:
> >
> > David, what you are using is a log(log(x)) representation internally.
> IEEE
> > is *not* linear, it is logarithmic.
>
> As Robert Kern says, yes, this is exactly what the OP and all the rest
> of us want.
>
> But it's a strange thing to say that IEEE is logarithmic - "2.3*10**1"
> is not exactly logarithmic, since the "2.3" is not the logarithm of
> anything. IEEE floats work the same way, which is important, since it
> means they can exactly represent integers of moderate size. For
> example, 257 is represented as
>
> sign 0, exponent 135, (implied leading 1).00000001b.
>
> The exponent is indeed the integer part of the log base 2 of the
> value, up to some fiddling, but the mantissa is not a logarithm of any
> kind.
>

First order in the  Taylors series. The log computation uses the fact that
it has small curvature over the range 1..2

Chuck
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