Syntax befuddlement

[Joe Koski]

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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