usage:
[psd,f_out] = pyulear(x,poles,freq,Fs,range,method,plot_type)

Calculates a Yule-Walker autoregressive (all-pole) model of the data "x"
and computes the power spectrum of the model.  This is a wrapper for
functions "aryule" and "ar_psd" which perform the argument checking.
See "help aryule" and "help ar_psd" for further details.

ARGUMENTS:
All but the first two arguments are optional and may be empty.
x       %% [vector] sampled data

poles   %% [integer scalar] required number of poles of the AR model

freq    %% [real vector] frequencies at which power spectral density
is calculated
[integer scalar] number of uniformly distributed frequency
values at which spectral density is calculated.
[default=256]

Fs      %% [real scalar] sampling frequency (Hertz) [default=1]


CONTROL-STRING ARGUMENTS -- each of these arguments is a character string.
Control-string arguments can be in any order after the other arguments.


range   %% 'half',  'onesided' : frequency range of the spectrum is
from zero up to but not including sample_f/2.  Power
from negative frequencies is added to the positive
side of the spectrum.
'whole', 'twosided' : frequency range of the spectrum is
-sample_f/2 to sample_f/2, with negative frequencies
stored in "wrap around" order after the positive
frequencies; e.g. frequencies for a 10-point 'twosided'
spectrum are 0 0.1 0.2 0.3 0.4 0.5 -0.4 -0.3 -0.2 -0.1
'shift', 'centerdc' : same as 'whole' but with the first half
of the spectrum swapped with second half to put the
zero-frequency value in the middle. (See "help
fftshift". If "freq" is vector, 'shift' is ignored.
If model coefficients "ar_coeffs" are real, the default
range is 'half', otherwise default range is 'whole'.

method  %% 'fft':  use FFT to calculate power spectrum.
'poly': calculate power spectrum as a polynomial of 1/z
N.B. this argument is ignored if the "freq" argument is a
vector.  The default is 'poly' unless the "freq"
argument is an integer power of 2.

plot_type %% 'plot', 'semilogx', 'semilogy', 'loglog', 'squared' or 'db':
specifies the type of plot.  The default is 'plot', which
means linear-linear axes. 'squared' is the same as 'plot'.
'dB' plots "10*log10(psd)".  This argument is ignored and a
spectrum is not plotted if the caller requires a returned
value.

RETURNED VALUES:
If return values are not required by the caller, the spectrum
is plotted and nothing is returned.
psd     %% [real vector] power-spectrum estimate
f_out   %% [real vector] frequency values

HINTS
This function is a wrapper for aryule and ar_psd.
See "help aryule", "help ar_psd".