%	This program is distributed as a supplement to the book
%	"Biomedical Signal Processing and Signal Modeling" by E. N. Bruce,
%	published by Wiley, 2000.  It is provided for educational use only.
%  While every effort has been made to insure its suitability to illustrate
%  principles described in the above book, no specific feature or capability 
%  is implied or guaranteed.
mmax=floor(log(length(x))/log(2));
sd(1)=std(x,1);
y=x; nsk=2;nl=2*floor(length(y)/2);
for m=2:mmax-nsk
   j=0;
   for k=1:2:nl
      j=j+1;
      y(j)=(y(k)+y(k+1))/2;
   end
   sd(m)=std(y(1:j),1);
   nl=j;
end
plot([0:mmax-1-nsk],log(sd(1:mmax-nsk))/log(2),'.')
arg1=[0:mmax-1-nsk]'-mean([0:mmax-1-nsk]);
arg2=log(sd(1:mmax-nsk)')/log(2)-mean(log(sd(1:mmax-nsk))/log(2));
slope=tls(arg1,arg2)
xlabel('log2(m)');ylabel('log2(SD(m))')
hcoeff=1+slope