bug report, or am I doing something wrong?

Hi Luke,

Firstly, although the "calculator" convention of log() vs ln() certainly
exists, there is a convention in most (if not all) mathematical programming
languages that log() is the natural log.  This holds for both numerical
(Matlab/Octave) and symbolic (Maxima/Mathematica/Axiom) languages.  From a
mathematician's standpoint, the natural log is the only "one true
logarithm", arising from calculus (arising from the integral of x^(-1)).
All others are defined as:

Log[base y](x) = ln(x)/ln(y)

In Maxima, for example, you can define:

log10(x) := log(x)/log(10);

After all, using logarithms to the base 10 is really just a consequence of
humans having 10 fingers.  So, I don't think you're going to get your
warning message about log() meaning natural log - it is a standard
convention.

Maxima function names are case sensitive, so LOG() is not the same as log().
If you really want to, you can do:

ln(x) := log(x);
LOG(x) := log(x)/log(10);

However, this probably asking for more trouble than just using log10() as
above.

-Frank


-----Original Message-----
From: maxima-admin at math.utexas.edu [mailto:maxima-admin at math.utexas.edu] On
Behalf Of Luke Sharkey
Sent: Friday, February 10, 2006 5:55 AM
To: maxima at math.utexas.edu
Subject: FW: [Maxima] bug report, or am I doing something wrong?


So does nobody have any feedback for me on the log question, etc.?



-----Original Message-----
From: Luke Sharkey 
Sent: 06 February 2006 11:01
To: 'maxima-admin at math.utexas.edu'
Subject: RE: [Maxima] bug report, or am I doing something wrong?

"Maxima's choice of branches for multi-valued functions."
So what can be done about it:  when can we know whether the calculated
integral / differential is more likely to be corrector not?  Am I just going
to have to plot it each time?


Also:  (this caused me a *lot* of headache before I realised what was going
on).  
Its about the log() function.  I checked the documentation, and finally
realised that log() actually means the *natural logarithm*.  


Firstly, how does one do log to the base 10 with maxima?
  
Secondly, on every calculator, maths program (Microsoft Excel, etc) and
textbook I have ever used, "log" has ALWAYS meant "log to the base 10", and
"ln()" log to the base e", unless it is specified in some way, e.g.
log2() meaning log to the base 2.  I propose that the "log" function should
be changed in meaning from natural log to log to the base 10.  I personally
think a new function should be created as ln() for natural logarithms.

At the very least, every time the log function is used, some text should
appear below indicating that the such and such a calculation involving a log
has been "calculated with log to the base xyz" underneath the output, so
people like me don't use it assuming that "log" means "log to the base 10".

Thirdly, programs like Excel use "LOG" in uppercase.  Maxima should be able
to recognise when "LOG" is typed, or copied and pasted in from Excel, that
it should be recognised as "log": this should be automatic.


Thanks.
L Sharkey
________________________________________
From: maxima-admin at math.utexas.edu [mailto:maxima-admin at math.utexas.edu]
On Behalf Of Robert Dodier
Sent: 31 January 2006 15:45
To: Maxima List
Cc: Luke Sharkey
Subject: Fwd: bug report, or am I doing something wrong?

A quick look suggests the results below stem from Maxima's choice of
branches for multi-valued functions. 


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