Re: Syntax befuddlement

[Joe Koski]

Henry,

Duh! Why didn't I think of that! Thanks for the suggestion. I should have
done your experiment myself, first.

When I try it I get:

octave:1> x=rand(1,8)
x =

  0.59183  0.29134  0.73197  0.63839  0.13084  0.81752  0.33805  0.69539

octave:2> t=[0.002:0.001:0.007]
t =

  0.0020000  0.0030000  0.0040000  0.0050000  0.0060000  0.0070000

octave:3> fnormhat=0.5*(angle(-x(t+1).*conj(x(t-1)))+pi)/(2*pi)
error: invalid vector index = -1
error: evaluating argument list element number 1
error: evaluating binary operator `.*' near line 3, column 28
error: evaluating argument list element number 1
error: evaluating binary operator `+' near line 3, column 43
error: evaluating binary operator `*' near line 3, column 13
error: evaluating binary operator `/' near line 3, column 47
error: evaluating assignment expression near line 3, column 9

Which is a duplicate of the errors that I get from within the routine. When
I make t an integer I get your result.

octave:6> t=[2:7]
t =

  2  3  4  5  6  7

octave:7> fnormhat=0.5*(angle(-x(t+1).*conj(x(t-1)))+pi)/(2*pi)
fnormhat =

  0.50000  0.50000  0.50000  0.50000  0.50000  0.50000

I'm not sure that the 0.5 is the correct answer, either.

I know how to calculate frequency (it's the difference of successive phase
angles in radians divided by something like 2*pi*dt). I can look at other
similar routines for guidance.

I just thought that maybe they had an elegant, quick method for doing it,
that I didn't understand. Everywhere else in those MatLab routines, t is a
real, not an integer. More experiments are in order. Thanks for the
suggestion.

Joe Koski



on 12/27/03 12:55 PM, Henry F. Mollet at address@hidden wrote:

> Thanks for earlier expose on octave for Mac/Fink/DarvinPort.
> 
> I've checked below statement with a simple-minded test using a real x and t
> and it worked but it may not be a meaningful test:
> octave:1> x=rand (1,10)
> x =
> Columns 1 through 7:
> 0.925892  0.410042  0.170498  0.240161  0.811388  0.024802  0.997211
> Columns 8 through 10:
> 0.773300  0.687108  0.668670
> octave:2> t = [2:9]
> t =
> 2  3  4  5  6  7  8  9
> octave:4> fnormhat=0.5*(angle(-x(t+1).*conj(x(t-1)))+pi)/(2*pi)
> fnormhat =
> 0.50000  0.50000  0.50000  0.50000  0.50000  0.50000  0.50000  0.50000
> Henry
> 
> on 12/26/03 8:14 PM, Joe Koski at address@hidden wrote:
> 
>> I'm trying to use a MatLab routine that I found on the net for calculating
>> instantaneous local frequency after a Hilbert transform. The hilbert.m
>> routine (called from octave-forge) completes successfully. The amplitude of
>> the signal is correctly calculated from the results. In attempting to
>> calculate frequency and convert the remainder of the MatLab routine to
>> octave, I get errors during execution terminating with:
>> 
>> error: invalid vector index = -1
>> 
>> The statement that is being evaluated at the time of the error is
>> 
>> fnormhat=0.5*(angle(-x(t+1).*conj(x(t-1)))+pi)/(2*pi);
>> 
>> where x is a real column vector (representing data) of length 256, and t is
>> a real row vector (representing time "instants," but with the first and last
>> values truncated) of length 254.
>> 
>> When I try this with the --braindead option, the routine gives no errors,
>> but then no results are returned, either. The date on this script is 1994
>> and it's currently posted on the web, so it probably really does work in
>> MatLab.
>> 
>> As an old Fortran programmer, the statement syntax seems very strange to me.
>> 
>> My questions: 
>> 
>> How can one real array with increments (t+1, t-1) be an index for another
>> real array (x)? Or does that indicate a functional relationship?
>> 
>> Is this standard octave?
>> 
>> Are there tricks for getting MatLab scripts like this to execute correctly
>> in octave?
>> 
>> Alternatively, are there an equivalent octave-forge routines that would
>> avoid the problem?
>> 
>> If it would help, I could include more of the routine.
>> 
>> Thanks.
>> 
>> Joe Koski
>> 
>> 
>> 
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> 
> 
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