From: Morton Goldberg <m_goldberg@...>
Date: 2007-02-08T14:00:28+09:00
Subject: Re: Adding Math.log2 and Math.logn to the core library.

On Feb 7, 2007, at 9:00 PM, Eric I. wrote:

> On Feb 7, 7:08 pm, Morton Goldberg <m_goldb...@ameritech.net> wrote:
>> Well, I can find examples with the base first or second. Perhaps for
>> Ruby it would most idiomatic to define log as follows
>>
>>     def Math.log(x, b=Math::E); ... ; end
>>
>> as the core method with log10 and log2 handled (for performance) as
>> special cases within this method. Given that, I would still want Math
>> to implement log10 and log2 methods for convenience.
>
> Math.log calls the log in the standard math library, which I suspect
> implements the natural log calculation pretty efficiently.  If you
> make the second parameter the base, you'll either have to check it
> against Math::E and treat it as a special case or do two log
> calculations for the natural log case.  I don't like either of those
> options.

If there's too much of a performance penalty for this, I would have  
no problem with the general case being implemented under a different  
name, and I would suggest "logb" -- that is,

    def Math.logb(x, b=Math::E); ... ; end

My main point is that I think the general case should default its  
base to Math::E. If we were to end up with Math.log (alias Math.ln),  
Math.log10, Math.log2, and Math.logb (the general case) that  would  
be fine.

Regards, Morton