logarithm with variable base eg. log9

[Alexander]

Hi all,

I have to include the "simple" term
m(i,j)= log9(m(i,j)) in my MATLAB code. Unfortunatelly I
cant find any function that calculates the logarithm with
base 9.

MATLAB supports log (base e), log10 and log2. But what's
about log9, log8, log7 and so on. I am sure there is a way
to calculate the logarithm with a variable base. But how?

Moreover the inverse function is possible. You can solve
y=9^x but not x=log9(y). That would be strannge?

I really hope somebody can help.

Thank you very much!!!!!

Regards,
Alex

[Amir]

Hi. Remember that when you want to calculate log base N,
you can calculate it in terms of any log function you have
(log10, log2, log base e).

So y = logN(x) also = logM(x)/logM(N) where M is ANY log.

For example, y=log9(x) = log10(x)/log10(9).

"Alexander " <sal...@gmx.net> wrote in message <g5gpn6
$glg$1...@fred.mathworks.com>...

[Roger Stafford]

"Alexander " <sal...@gmx.net> wrote in message <g5gpn6$glg
$1...@fred.mathworks.com>...

---------
It's not very hard to write log(x)/log(b) in place of log_base_b(x). Or if it
occurs very often, you can even write a two-argument function to do the
same thing.

Roger Stafford

[Walter Roberson]

In article <g5gpn6$glg$1...@fred.mathworks.com>,
Alexander <sal...@gmx.net> wrote:

>Moreover the inverse function is possible. You can solve
>y=9^x but not x=log9(y). That would be strannge?

If you have the symbolic toolbox, you can solve('x=9^y','y');
--
"He wove a great web of knowledge, linking everything together,
and sat modestly at a switchboard at the center, eager to help."
-- Walter Kerr

[Alexander]

Hi there,

Thanky you very much for the helpful answers. Problem is
now solved. Thanks :-)