function [y,flag]=secant(f,y0,y1,tol)
%  function [y,flag]=secant(f,y0,y1,tol)
count=0;
quit = 0;
flag=0;
y=y0
yold=y1
x=zeros(1,20);
fyold=eval([f,'(yold)'])
while quit ==0 
  fy=eval([f,'(y)'])
  diff=fy*(y-yold)/(fy-fyold)
  yold=y
  fyold=fy
  y=y-diff
  m=tol;
  if abs(y)>m
    m=abs(y) 
   end;
  if abs(y-yold) < m*tol
    quit=1
  end;
  count=count+1
  x(count)=y;
  if count >19 
    quit=1;
    flag=1;
  end;
end;
x(1:count)