givsturm.m

various matlab programs to slove various problems

function [ak,bk,ck,nch,niter]=givsturm(dd,bb,ind,toll)
[a, b]=bound(dd,bb); 
dist=abs(b-a); 
s=abs(b)+abs(a);
n=length(d); 
niter=0; 
nch=[];
while (dist > (toll*s)),
    niter=niter+1; 
    c=(b+a)/2;
    ak(niter)=a; 
    bk(niter)=b; 
    ck(niter)=c;
    nch(niter)=chcksign(dd,bb,c);
    if (nch(niter) > (n-ind))
      b=c;
    else
      a=c; 
    end; 
    dist=abs(b-a); 
    s=abs(b)+abs(a);
end
return