You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: distitpf.m
    path of file: ./repos/VAD/lib/matlab/voicebox
    
    the code of the file until where you have to start completion: function d=distitpf(pf1,pf2,mode)
%DISTITPF calculates the Itakura spectral distance between power spectra D=(PF1,PF2,MODE)
%
% Inputs: PF1,PF2     Power spectra to be compared. Each row represents a power spectrum: the first
%                     and last columns represent the DC and Nyquist terms respectively.
%                     PF1 and PF2 must have the same number of columns.
%
%         MODE        Character string selecting the following options:
%                         'x'  Calculate the full distance matrix from every row of PF1 to every row of PF2

    
function d=distitpf(pf1,pf2,mode)
%DISTITPF calculates the Itakura spectral distance between power spectra D=(PF1,PF2,MODE)
%
% Inputs: PF1,PF2     Power spectra to be compared. Each row represents a power spectrum: the first
%                     and last columns represent the DC and Nyquist terms respectively.
%                     PF1 and PF2 must have the same number of columns.
%
%         MODE        Character string selecting the following options:
%                         'x'  Calculate the full distance matrix from every row of PF1 to every row of PF2
%                         'd'  Calculate only the distance between corresponding rows of PF1 and PF2
%                              The default is 'd' if PF1 and PF2 have the same number of rows otherwise 'x'.
%           
% Output: D           If MODE='d' then D is a column vector with the same number of rows as the shorter of PF1 and PF2.
%                     If MODE='x' then D is a matrix with the same number of rows as PF1 and the same number of columns as PF2'.
%
% If ave() denotes the average over +ve and -ve frequency, the Itakura spectral distance is 
%
%                               log(ave(pf1/pf2)) - ave(log(pf1/pf2))
%
% The Itakura distance is gain-independ