在matlab中像buttord,butter,pburg这些函数是已经定义好的吗？可以直接用吗？

function varargout = pburg(x,p,varargin)
%PBURG Power Spectral Density (PSD) estimate via Burg's method.
% Pxx = PBURG(X,ORDER) returns the PSD of a discrete-time signal vector X
% in the vector Pxx. Pxx is the distribution of power per unit frequency.
% The frequency is expressed in units of radians/sample. ORDER is the
% order of the autoregressive (AR) model used to produce the PSD. PBURG
% uses a default FFT length of 256 which determines the length of Pxx.
%
% For real signals, PBURG returns the one-sided PSD by default; for
% complex signals, it returns the two-sided PSD. Note that a one-sided
% PSD contains the total power of the input signal.
%
% Pxx = PBURG(X,ORDER,NFFT) specifies the FFT length used to calculate
% the PSD estimates. For real X, Pxx has length (NFFT/2+1) if NFFT is
% even, and (NFFT+1)/2 if NFFT is odd. For complex X, Pxx always has
% length