precalculus does matter

[trochee]

I just spent three days working out why two different language modeling schemes were producing vastly different log-probabilities. I was using every bit of good software design practice that I know, and leaning on colleagues to confirm that I was running it right.

You know why it all went wrong? System X produces probabilities in logarithms of base 10, and system Y does it in base e.

This reminds me of the stories about the Mars Climate Orbiter unit conversion error, although that is apparently apocryphal.

Comments

[evan.livejournal.com]

shouldn't log_e and log_10 just be off by a constant multiplier?

[trochee.livejournal.com]

yup, they're different by a constant multiplier of log[e](10). But when you're log-linearly interpolating between the log values it matters.

[kirinqueen.livejournal.com]

From what I hear, that is a relatively common cause of calculation bugs. No less silly, perhaps, but it's not so ridiculous to just think of log as log.

[trochee.livejournal.com]

*sings*

it's log, it's log
it's big, it's heavy, it's wood
it's log, it's log
it's better than bad -- it's good

[bwb-archive.livejournal.com]

At last! You have said something I understand!

[boobirdsfly.livejournal.com]

I concur... and... this song would please the log lady in Twin Peaks very much. trochee , you sure have been thinking in songs lately... and you're quite good at it !:)

[trochee.livejournal.com]

heh. It's not my song.

[boobirdsfly.livejournal.com]

I remember Ren and Stimpy. I spent hours when i first moved to the US sitting in a living room with people laughing really hard and not understanding what was so funny. Now i get it !
It did sound kinda familiar but i thought you adapted it from something... :)

[q-pheevr.livejournal.com]

Funny, I always thought the lyrics went like this:

It's ln, it's ln,
It's it's big, it's heavy, it's wood!
It's ln, it's ln, It's better than bad—it's good!

[trochee.livejournal.com]

hahah!

[congogirl.livejournal.com]

Yay! This refrain and the Fish Heads one occasionally sprint through my head when I'm not paying attention...



[{refrain}fish heads fish heads, roly poly fish heads, fish heads fish heads, eat them up, YUM! {verse}you can take a fish head / to a movie / wouldn't have to pay to / get - it - in!}]