Re: Hilbert transform y = hilbert(x,n)

[John B. Thoo]

On Jun 9, 2009, at 11:35 AM, Dmitri A. Sergatskov wrote:

> On Tue, Jun 9, 2009 at 9:35 AM, John B. Thoo<address@hidden> wrote:
> > Hello, everyone.
> >
> > A friend sent me some code he had written for the "dark side."  When
> > I tried to execute it in Octave, I got the error
> >
> > error: `hilbert' undefined near line 11 column 8
> > error: evaluating assignment expression near line 11, column 6
> > error: called from `psidot' in file `/Users/jbthoo/Desktop/
> > NumMethPractice/BurgersHilbert/psidot.m'
> > error: called from `rk_step' in file `/Users/jbthoo/Desktop/
> > NumMethPractice/BurgersHilbert/rk_step.m'
> > error: evaluating for command near line 93, column 5
> > error: evaluating for command near line 91, column 1
> > error: near line 101 of file `/Users/jbthoo/Desktop/NumMethPractice/
> > BurgersHilbert/run_amp.m'
> > octave-3.0.5:4>
> >
> > When I looked in the file "psidot.m", I saw near the beginning the  
> > line
> >
> > hpsi = hilbert(psi,lx);
> >
> > so I googled "octave hilbert".  This led me to two definitions of
> > "hilbert":
> >
> > <http://sccn.ucsd.edu/pipermail/eeglablist/2006/001257.html>
> > <http://www.nabble.com/Hilbert-transform-m-file-contribution-
> > td9238169.html>
> >
> > However, both of them define
> >
> > y = hilbert(x)
> >
> > of one argument instead of two as called in "psidot.m".
>
> hilbert is part of the octave-forge signal-1.0.8 package :
>
>
>
> octave:1> help hilbert
>  -- Function File: H = hilbert (F,N,DIM)
>      Analytic extension of real valued signal
>
>      `H=hilbert(F)' computes the extension of the real valued signal F
>      to an analytic signal. If F is a matrix, the transformation is
>      applied to each column. For N-D arrays, the transformation is
>      applied to the first non-singleton dimension.
>
>      `real(H)' contains the original signal F.  `imag(H)' contains the
>      Hilbert transform of F.
>
>      `hilbert(F,N)' does the same using a length N Hilbert transform.
>      The result will also have length N.
>
>      `hilbert(F,[],DIM)' or `hilbert(F,N,DIM)' does the same along
>      dimension dim.
>
> /usr/share/octave/packages/signal-1.0.8/hilbert.m
>
> Additional help for built-in functions and operators is
> available in the on-line version of the manual.  Use the command
> `doc <topic>' to search the manual index.
>
> Help and information about Octave is also available on the WWW
> at http://www.octave.org and via the address@hidden
> mailing list.
> octave:2>
>
> > How can I modify either of the two definitions that google returned
> > so that I can execute my friend's code?
> >
> > Thanks.
> >
> > ---John.
>
> Hope that helps,
>
> Dmitri.

Hi, Dimitri.  Thanks for the tip.  I duly installed  
"signal-1.0.10.tar.gz" (after installing the dependencies  
"miscellaneous-1.0.9.tar.gz" and "optim-1.0.6.tar.gz").  Then I ran  
"run_amp" again.  Now I get this error:

error: HILBERT only works for real-valued signals.
error: evaluating if command near line 47, column 3
error: called from `hilbert' in file `/Users/jbthoo/octave/ 
signal-1.0.10/hilbert.m'
error: evaluating assignment expression near line 11, column 6
error: called from `psidot' in file `/Users/jbthoo/Desktop/ 
NumMethPractice/BurgersHilbert/psidot.m'
error: called from `rk_step' in file `/Users/jbthoo/Desktop/ 
NumMethPractice/BurgersHilbert/rk_step.m'
error: evaluating for command near line 93, column 5
error: evaluating for command near line 91, column 1
error: near line 101 of file `/Users/jbthoo/Desktop/NumMethPractice/ 
BurgersHilbert/run_amp.m'
octave-3.0.5:10>

so I edited the following line in "psidot.m"

hpsi = hilbert(psi,lx);

to

hpsi = hilbert(real(psi),lx);

and it runs without any error complaints.  Yea! :-)  Now I only hope  
that (inserting "real") was the right thing to do.  Was it?

BTW, on the "dark side" I don't get the complaint that "HILBERT only  
works for real-valued signal"; instead, I get the warnings:

Warning: HILBERT ignores imaginary part of input
> In hilbert at 39
  In psidot at 11
  In rk_step at 10
  In run_amp at 94

but the program continues.

Thanks again.

---John.