MATLAB: How to resolve between @spectrum/psd.m and psd.m

built-in-functionclass methodresolve ambiguity

Hi,
In Spectral Analysis http://www.mathworks.com/help/toolbox/signal/ug/f12-6587.html, under Nonparametric Methods>> Periodogram, the following code snippet is shown
fs  =  1000; %  Sampling  frequency
t  =  (0:fs)/fs; %  One  second  worth  of  samples
A  =  [1  2]; %  Sinusoid  amplitudes  (row  vector)
f  =  [150;140]; %  Sinusoid  frequencies  (column  vector)
xn  =  A*sin(2*pi*f*t)  +  0.1*randn(size(t));
psd(Hs,xn,'Fs',fs,'NFFT',1024,'SpectrumType','onesided')
I am curious on which function psd is, so I used which to locate it:
>> which psd
C:\Program Files\MATLAB\R2008a\toolbox\signal\signal\psd.m
>> which spectrum.psd
C:\Program Files\MATLAB\R2008a\toolbox\signal\signal\@spectrum\psd.m % static method or package function
It seems that “which psd” returns a standalone function, whereas “which spectrum.psd” returns a static function of the spectrum class.
In standard Object-oriented programming language like C++, compiler examines argument list to resolve overloaded functions. But here,
Standalone psd.m;
function [Pxx, Pxxc, f] = psd(varargin)
@spectrum\psd.m:
function varargout = psd(this,x,varargin)
both take variable input argument lists, and the calling statement
psd(Hs,xn,'Fs',fs,'NFFT',1024,'SpectrumType','onesided')
has no return argument which, if length ≥4, could possibly be used to resolve ambiguity since standalone psd.m has maximum of 3 outputs.
So how could the compiler determine which psd.m is executed, the standalone one or the spectrum class method under @spectrum?
Bob

Best Answer

For
...
Hs = spectrum.periodogram;
psd(Hs,xn,'Fs',fs,'NFFT',1024,'SpectrumType','onesided')
MATLAB knows to call the spectrum.psd method sicne the first argument is of class spectrum.
I don't have access to MATLAB right now, but if instead you do
...
eval('Hs = spectrum.periodogram;');
psd(Hs,xn,'Fs',fs,'NFFT',1024,'SpectrumType','onesided')
I am pretty sure you confuse the JIT and you get the psd function.
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