Re: [Discuss-gnuradio] nlog10: do we consider "normalizes log10(x <= 0) to -18" as API?

On 11/20/2017 07:52 AM, Marcus Müller wrote:
> Hi Folks,
>
> I was about to commit a PR VOLKizing nlog10 [1], but it struck me that
> my processor (imho, correctly) says that log(0) == nan and log(-10) ==
> nan.
>
> Whereas the old nlog10 test case asserts that it's log_10(x<=0) == -18.

It would have to be complex

y=log10(-.00000000000000000001)
y=-18 + 1.3644i

For x real, then the limit as x approaches 0 from the positive side is
-infinity.

For x real from the negative side it's undefined since for any y, 10**y > 0.

-- Cinaed

>
> So, am I allowed to break that assertion for the greater mathematical
> appropriateness and speed?
>
> Best regards,
> Marcus
>
> [1]
> https://github.com/marcusmueller/gnuradio/tree/blocks_volkized_nlog10
>
>
>
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