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How to get the log of an expression as a sum of logs?

Xuinkr Bin
Posted 11 years ago
POSTED BY: Xuinkr Bin
6 Replies
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Jim Baldwin
Jim Baldwin, Retired
Posted 11 years ago

There's a discussion of something very related at Mathematica StackExchange.
POSTED BY: Jim Baldwin

You are looking for PowerExpand:

Log[a b c] // PowerExpand
(* giving:  Log[a]+Log[b]+Log[c] *)

Henrik
POSTED BY: Henrik Schachner
Xuinkr Bin
Xuinkr Bin
Posted 11 years ago

While I think this answer is correct, when I use c in the expression, I get negative infinity. Replacing c with d works. Is c considered a "special variable" of some sort?
POSTED BY: Xuinkr Bin

Hi Xuinkr Bin,

no, c hast no chance of being a special (i.e. system-) variable. Only variables beginning with a capital letter can have such a meaning. Begin your notebook with the command

ClearAll["Global`*"]

or with a fresh kernel and try again.

Regards Henrik
POSTED BY: Henrik Schachner
Juan Miranda
Juan Miranda
Posted 11 years ago

This is what you want to do?

y = abc; log = Total[Map[Log[#] &, y[[1 ;; -1]]]]
POSTED BY: Juan Miranda
Xuinkr Bin
Xuinkr Bin
Posted 11 years ago

Maybe. I'm not familiar enough with the notation to say for certain one way or another.
POSTED BY: Xuinkr Bin
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