Presume I have an expression, a x b, and want to take the log, seeing it is log(a) + log(b). What function should I use? I would have thought Log would be the right one but it does not seem to do that; I get back Log[a b].
There's a discussion of something very related at Mathematica StackExchange.
You are looking for PowerExpand:
Log[a b c] // PowerExpand
(* giving: Log[a]+Log[b]+Log[c] *)
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?
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
or with a fresh kernel and try again.
This is what you want to do?
y = abc;
log = Total[Map[Log[#] &, y[[1 ;; -1]]]]
Maybe. I'm not familiar enough with the notation to say for certain one way or another.