Re: Calculating log for each array element

[Jaroslav Hajek]

On Fri, Jun 20, 2008 at 2:40 PM, DimitryASuplatov <address@hidden> wrote:
> Hello,
>
> I have array with some values initialized as
>
> a = load <filename>
>
> I want now to create another array b so as b[i] = log(a[i])
> I do this as follows
>
> for i = 1:length(a)
>        b(i) = log(a(i))
> endfor
>
> This works but it takes to long
>
> 1/ Is there any way to speed this up?
Try
b = log(a);
(semicolon means the result is not dumped to screen)

> 2/ How to convert my array a to list?
In general, there is no need. Arrays are dynamic, so they can grow as needed,
although it is usually beneficial to pre-allocate if you can. You can
use cell arrays
if you want to.

> 3/ How to append to array?

Use array constructor, "*cat", or simply assign out of bounds. All the
following expressions append "x" to a row vector "array":
array = [array,x];
array = horzcat(array, );
array(end+1) = x;

Note that Octave distinguishes column vectors and row vectors, as in
linear algebra.
Sometimes the distinction matters, sometimes not.

>
> I really appreciate your help!
> Thank you!
>
> SDA
>
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>



-- 
RNDr. Jaroslav Hajek
computing expert
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz