function [z] = soundfile(y,varargin)
%"Song of convergence" Copyright Andrew Knyazev 1998 
%Z=soundfile(Y) takes the colunm-vector Y
%with components describing history of convergence
%of an iterative method and returns a file Z that
%can be played with sound(Z) command. 
%Convergence is assumed to be close to linear.
%The program will take first two columns 
%of Y, if Y has more then one column.
%That will produce a stereo sound, is supported
%by user's hardware.
%The default playing time is about a second
%on my computer. It can be changed by using an
%optional scalar input argument,
%Z=soundfile(Y,length). Reasonable range of length
%is between 0.1 and 3. 
%Example:
%q(1,1)=1;q(1,2)=1;
%for i=2:100
%q(i,1)=0.99*q(i-1,1);
%q(i,2)=0.89*q(i-1,2);
%end
%s=soundfile(q,2);
%sound(s);
%will play a stereo sound for ~2 seconds.
nin = max(nargin,1)-1;
if nin>0 
   length=cat(nin,varargin{:});
else 
   length=1;
end
if length > 3
   disp('The value of the optional argument is too big')
   disp('The program soundfile may take forever to execute')
   disp('Enter the number again,') 
   an=input('or just press "Enter" to use the default "1":');
     if isempty(an)   
        length=1
     else
        length=an
     end
end
[n,nchannel]=size(y);
nchannel=max(2,nchannel);
y=log(y);
maxy=max(max(y));
miny=min(min(y));
y=(y-miny)/(maxy-miny);
x=(1:n)'/n;
size=round(length*10000);
xi=(1:size)'/size;
yi=interp1(x,y,xi,'*linear');
for i=1:size
   for j=1:nchannel
      z(i,j)=sin(size*xi(i)*(1.2+yi(i,j)));
   end
end